You may want to verify that your DE allows rentals. The SE-R Conventions are the only DE's that I have attended that allowed rentals - Porsche, Audi, & BWM events are more local to me and they typically do not allow rentals.
Brakes and tires would probably be the downfalls to the rentals (since they will probably be all-seasons & quiet/non-squeaking brakes) - just thinking about standard rentals not S2000's, EVO's, etc.
HPDEs run by larger regional orgs (that aren't associated with car clubs) don't really seem to care. Tyres and brakes, as Fosters said, would be the primary concern if you're running in HPDE 2 or higher. Don't push too hard near the end of your sessions or Avis might ask you about the chunked shoulders.
On the other hand, the lack of overall grip and the less aggressive brakes might teach you something new. Who knows? It might even be a productive exercise.
I rented a Mini Cooper S for the SERCA National Convention the last time it was in So. Cal. The tires and brakes held up really well, rental agency never said anything, and I found out how well the Stability Control System works to keep the car from spinning around in transitions.
Thanks for the responses guys. Kind of what I was thinking. I don't see an issue and I am not going to push too hard. I am one of the technical inspectors for the event so the car will get in. I am going to replace the brake fluid with some ATE Gold fluid. Should be fine. I just don't really like the track too much so I am going for the Saturday night pig roast and help with tech. More of a social weekend. Race car is staying home.
It doesn't have that racey name for nothing... Yes, it's high centered. Just lean forward and it comes off...
I've run rentals (as most of you know) at many, many, many events. As long as you don't go shouting to the world that it's a rental, most don't say anything.
Rentals generally aren't fast enough, nor have good enough tires to boil the brakes. Plus, since they're not your tires, you can always just trail brake instead to scrub speed.
Stay away from the Mazda 6 (or probably any automatic Mazda). The damned near self-aware computer would determine I was abusing the car too much and take away the manual gear select function and shift straight to 6th. This is a major problem when the first time you discover this is going really hot into turn 8 at Willow Springs. Nothing like 100+mph 4 wheels drifts with no cage, a wall close enough, and no way to correct it in time with the gas pedal. Yikes!
Oh, I would also disable the ABS. If (when) you go off track, ABS is nearly worthless in the dirt (read: NEARLY NO BRAKE APPLICATION WHATSOEVER). Since you're always told to go both feet in (well, one foot with an automatic) when you go off track, this can get, err, exciting?
ya know... I still have some pics of the tires from that Buick I would say, get something small like the Focus. Also, like Rockwood said, you don't need to worry about the brakes. Rentals are too damn slow anyways.
The deficiencies of a street car are so amplified at the track. Luckily it made good power. Thing worked well at the skidpad. Had a good weekend. Buddy bought a Radical SR3 and let me drive it for a session. We were both in the 1:30's at Shenandoah right away which is pretty decent with no seat time and no setup.