I haven't been to a challenge (want to eventually, but maine is a long way away), but I will provide my feedback anyway.
Tires - For fairness' sake, I like the idea of a spec tire, or making them free from the budget, but how do you make it work? If you spec an ST-type tire, the sizes are limited and you'll be ruling out a lot of cars right out of the gate. If you spec an A6 or V710, you might be doubling the build budget for a lot of teams. If you spec some other cheaper R-comp, it will probably suck at autocross, and who wants to pay for a brand new set of tires that aren't even good at the thing you're using them for? An open tire budget makes sense for something like Lemons, because the tires have to last and be safe for a whole race, but for the challenge they only have to survive a few autocross runs.
Shipping -I agree that shipping costs should not have to ding the budget. It's already bad enough that more remote/northern members have to spend a lot more (time and money) just to get to the event, but it's even less fair if I also have to kill my budget to go down south and get a clean shell to build up. It also seems inconsistent to include shipping, but not the costs of getting the vehicle to the event. The ebay nonsense should fix itself somewhat now that ebay is requiring sellers to collect fees on shipping costs, and frankly let people throw as many 99 cent ebay junk parts at the car as they want, I bet the winning cars won't be.
UTCC - I love the idea of aligning the challenge with the UTCC, although I don't think that should replace the current event. I would be a lot more likely to attend a UTCC challenge, both based on geography and the fact that I'd much rather build a car for autox/track than drag racing. I suck at drag racing, I think it's boring, and things seem to break on dragstrips at about 100X the rate that things break at autox or track days. That said, I absolutely love seeing projects like Andy's bug and it would suck a lot if the drag oriented projects went away. 1/4 mile times are also a great way to sell magazines, and to convince casual observers of the awesomeness of the vehicles that get built for this event.
RallyX - give it up, guys. I love rallyx, but I don't even think it would be safe to take most of the existing challengers to a rallyx. For one, it would eliminate the open cars right off. I know rallyx suspensions don't have to be sophisticated, but they'd still have to be drastically different than a good autox setup. I think the biggest strike though is the fact that low traction equalizes cars to a great degree. This is a car building competition, not a driving one, and most rallycrosses I have been to, a great driver in a slow stock FWD or AWD car on rally tires can set FTD. You'd also have to use rallyx type cumulative scoring to be fair due to the surface variability affecting times, and that precludes being able to have pro drivers or multiple team members run for the best times. Rallyx is a lot of fun, but it just doesn't mesh well with a car building competition, especially if you expect those cars to be able to do anything other than rallyx.