scathing

Think about what you said, which is "yes but only if X, Y, Z". In other words, the answer to "is wider better" is actually "maybe". In practical terms, if you want to improve grip then changing the tyre compound and construction is far more noticeable, and with far less caveats, than changing the width.

If your car used to run the same sized tyre all round, and you run tyres with different circumferences front to rear then you can affect your traction / stability control and ABS (since they all rely on wheel rotation). Since that circumference is also not the same as stock, your speedo will also be out. Staggering tyres is only useful if your car makes enough power to actually overwhelm the grip in the dry. In the wet, wide tyres is a negative to grip. Tyre compound and design will also make a bigger difference to grip and handling than the width. Buy a better tyre, not a wider tyre, if you want grip. Unless you run a massively different tyre size, the aesthetics aren't even noticeable.

Depending on when, I might bring the Z out.

What Zebra said. The whole point of the exhaust-blown diffusers is that the ECU on the F1 motor keeps the thing at WOT even when braking, creating airflow when speed drops. At high speeds, the exhaust gas is a rounding error compared to the air flowing around the car. Unless the guys here have programmed the ECU to put the slusho in neutral every time the driver lifts off and have it keep the electronic throttle open, and then re-engage gears when the driver picks the throttle up, it won't be doing what the F1 guys are doing. If that's their aim I hope they've got mates at Mercedes who can tell them how to program the gearbox computer - changing from neutral into gear while rolling seems to be a good way to destroy the box, the gearbox has to know to select the appropriate gear for the ground speed, and it has to react almost instantaneously.

To keep your ride near where it is now, sway bars are the best option. You'll find the car skips a little more around the bends, but the improvement in chassis response more than makes up for it. As a NA 350Z owner, I'm not entirely sure what you're talking about. The Z has more grip than grunt. It does have axle tramp issues off the line due to the suspension geometry, and that's basically unfixable since its a function of how much camber the rear gets when it squats, but around the corner its got a crapload of grip in the rear. At the limit it does wash the nose if you're not progressive on the throttle, but getting rid of the staggered tyre setup fixes that (you will lose TCS/VDC but ABS still works). The thing doesn't start to oversteer unless you deliberately provoke it, and to keep it sliding once it breaks loose you have to keep clutch kicking. Fair enough if you're doubling the power and torque by going to a TT kit then you'll find you have traction issues, even with R-Comps, but that's true for any 2WD car. You can't pin that as a "350Z" or FM platform issue. If you don't take the car on the strip or circuit that often, and you just want a suspension setup for the winding road, I'd recommend doing adjustable swaybars first. If you're still finding it a fraction too soft for your tastes, then get a set of 350Z springs with Koni Yellow adjustable dampers. I've ridden in a few Zs with quite a few aftermarket suspension setups (Cusco, Zeal, Tein, Bilstein, HKS) and my favourite for street use was when I had OEM 350Z springs with Koni Yellows and adjustable swaybars. Does your car have the LSD? I know that, historically, viscous LSDs have copped a bad rap, but the one in the FM platform cars actually works quite well. If you can't afford to buy a Quaife, and I'd avoid all the clutchpack LSDs for street use, then make sure your car has at least the OEM VLSD.

NSW's is different. People have posted up links to the RTA web site that should answer all the OP's questions.

They don't necessarily need to be DOT approved. If they're compliant with: e(3) - european DOT - american JIS - Japan. And, even more confusingly, the current ADRs for tyres don't even require that the approval rating's mark be present anymore: http://www.performanceforums.com/forums/showthread.php?67224560-ADR-Approved-Tyres.-What-DOT-marking

Everything needs to be a bit cheaper.

Just because you've got dollars doesn't mean you've got sense. A significant number of modern M3 owners couldn't give two shits about owning one of the best handling coupes in the world, they just want everyone to see them driving it. That's why the current M3, with its giant V8, specific exhaust and body, and luxury trim, is a complete kick in the balls to the small I4, stripped out, barely noticeable from stock E30 M3 that started the legend. Now that they've blown so much cash on a car they will never truly appreciate, they're too cheap to spend up on accessories whose performance means even less to them than half the gadgets in the car, or the spirit of the original. Its quite easy to tell that a badged 320CI isn't an M3 these days, but most people wouldn't be able to pick the VMR 710 from the BBS CH. For them, that's more important to the handling benefits from stiffer wheels and less unsprung weight.

Really? The split spoke and mesh spoke designs were pioneered by BBS; basically everyone who's done it since has basically been copying them. Tempe sells a copy in 19", but I've got no idea what the offset is. Probably shithouse, being Tempe. But you could buy them and respray them. The DTM 073 is also another copy.

I've got a B&M short shifter in my 350Z, that I got from the US. The length is the same, but changing the pivot point reduces the throw. It rattles at certain RPM and it makes the shifter a lot heavier, but I like the shorter throw. It reminds me of the S2K's shifter, but less smooth.

Solution:

As far as I'm aware the OEM studs are 40mm long. Nismo sells 50mm and 60mm studs.

Love it.

Government-regulated attention in emissions is there, but that doesn't mean the engines aren't producing more power than they were for a given displacement or per unit of fuel. A big change has been thanks to the improvement in electronics, both in terms of performance and cost, which has let motors react more quickly to a greater amount of input data. That's allowed them to tune engines closer to the limit without compromising reliability. Aside from emissions its managed to both reduce fuel consumption of the engine itself and increase power (heavier chassis offsetting those gains notwithstanding since we're talking about engine tech). If you think about the last time the automotive world went on a big ecomentalist kick, it choked every engine that came out. These days power outputs relative to displacement or fuel consumption has still increased even though emissions regs are getting tighter. Not with an RB block, which is 20+ years old from an engineering standpoint, but it they were to engineer a modern "halo model" turbocharged 2.6L engine block today that complied with current emissions regulations it would still make more power, and be less laggy, than what an RB26DETT actually made (since we know the 280ps figure was basically porkies). It probably wouldn't hit 400kW but it would still make a fair amount of power. If you have a look at the VR38DETT, it makes a conservative 360kW, modern engine tech is not looking too bad. If we linearly scale up via displacement, and use a 320PS power figure for the RB26DETT instead of 280PS, then 3.8/2.6 * 320 = 470PS. The first-gen VR38 made 485PS, and that figure is just going to increase. Of course, we know that power doesn't increase linearly with displacement and so the true power gain due to developments in powerplant technology is more than just that small fraction.