ideas to generate revenue
How about incorporating a club at the local track, with annual dues. You have to be a member of the club to race, and of course you also have to pay the race entry fee to race. This way, the shop can make some money up front from anyone who wants to race. This is similar to the roar membership to race at roar sponsored events. The club fee can be $30-$40 for the year and include 3 practice sessions. (Practice costs the track very little, since the shop is open anyway.)
How about making the race fee $20 and have it cover up to 2 classes. This would do 2 things:
1) give the impression that racing is cheaper (most run 1 class and even adding 1 or 2 more heats to each round is not a big deal)
2) make more money per racer
3) sell more parts
Make certain classes run controlled hand out tires and motors. (The shop picks the brand, gets heat/fuel proof stickers made (inexpensive), and sell the tires/motors to the racers.) Allow anything in practice.
The 3 things above would increase the revenue from each racer by 30% or more and encourage more practice, which encourages more purchases.
If I were a hobby shop, I wouldn't stock race caliber equipment. For r/c, I would stock RTR r/c products and only consumables and limited parts for the cars being raced. I would special order everything else for each racer. Even though the markup on big items is small, the markup on small items (replacement parts,) is good (50%-100%). It doesn't make sense to carry inventory for products you rarely sell. (I am taking into account that racers buy online/used.)