I wish I had some before-after to show you guys how far gone you can still 'fix' a leather steering wheel. My N14 wheel I had written off and been wanting to get re-covered. I figured I was gonna re-condition/re-dye the R34 wheel, and so I'd give the N14 a go for a laugh, and I'm honestly stunned at how well it's come up.
I used the product from PPCCO - http://www.ppcco.com.au/kits6.htm
Damn cheap really, though lots of prep work with various treatments, sanding, filler, etc depending how far it's gone. I figured for $50 it was a cheap chance to have a go and see if it would work rather than forking out $250+ on the two wheels on my cars .. Eh, hey - each to their own. I don't mind trying a bit of DIY - figured I couldn't be in a worse position if I messed it up.