as you said if you get r33 you can spend money on other things, unless its a series 2 you will need a body kit IMO, but R34 looks fine stock !
As far as fuel economy goes the NEO is supposed to be more efficient, and the 34 has more power so should be faster, but i havent driven either so cant speak of which feels more responsive. Maybe someone with experience in both can shed some light on if the 34 has slightly more lag ?
a 34 WILL beat a 33, but if you just want to feel like your going fast, then if it turns out a 33 is more responsive maybe thats better for you ?
basically i think if youve had a 34 before and your having to second guess it maybe you really want the 33 so you can do more stuff to it, so perhaps that is your answer ?