I don't really think so, until you get to Elite level when you're going to know exactly what you like! In my humble opinion, I think that people use 7ft v 8ft rocker as an excuse to buy different blades in the hope that it will magically change whatever problem they are having with their skating, usually spinning. Once you're on a good blade with a decent spin rocker, technique is the thing that fixes that. Note that the spin rocker is different from the blade rocker!
This is definitely a good point - I think the spin rocker makes more of a difference than the main rocker when you're learning. My turns and spins improved quite a bit when I switched from the Ultima Mirage (8') to the MK Pro (7'), but I think it had much more to do with the fact that the MK Pro has a much more pronounced spin rocker. Some folks say 8' blades give you better stability and more glide, but I can't say I really noticed much of a difference there.
You use the spin rocker for spins, turns, and edge jump takeoffs, so when you're learning those skills, it's important that you have a spin rocker you can really feel so you can learn good blade placement.