There is a firewall to shock tower brace that is part of the reinforcement package for both level 1 and 2, but it is high enough up to not be an interference item with any size tire.

Speaking of tires, going to 17s is only going to net a small increase in performance compared to a good 15" tire. You'll probably see a better increase with the lighter weight 17" wheels than actual road holding power from 17" rubber. Light weight 15" wheels with sticky rubber is still a good match for a 17.

The biggest increase in driving performance comes from the suspension system. Look at it this way, changing a good 15" set up to a 17" set up is much like changing a 2.5" exhaust to a 3" exhaust. You'll gain some performance, but not a huge amount for the amount of cash outlay of the change. Upgrading your entire suspension system is like swapping out a low compression smog motor for a purpose built performance mill, the difference is huge.

Good gripping, 15" tires are available from Goodyear, Hoosier, Avon, American Racer, Towel City, and Mickey Thompson. Speed ratings are still available in S, T, H, V, and Z depending on vendor and size. Pricing is, unfortunatly, getting up there and is comparable to cheap 17" tires now.