Hi Pegasus,
I think the current format works, maybe there could be 3 daily races as El Barto mentions, but I think the variety is important to attract new players to compete.
I'm pretty sure, by now, most players use track and car mods, it's what has kept the game alive for so long.
Some of my favourite tracks are Oesterreiching 1979, Thruxton, Road Atlanta, Riverside, VIR, Bridgehampton, Oulton park, Longford, Phillip Island, Mont Tremblant, Croft, Snetterton, Melbourne (Albert Park), Nemuno Ziedas, Sebring, Motopark, Zwartkops Raceway, Deep forest race way, Dragon Tail, Glendale, anything by the Reboot team, and of course Fat Alfie - but they maybe a bit long for HLapping, Kicevo -for carting. The list goes on....
As for cars... I tend to lean towards historic so the GPL cars are just amazing, the ACL GTR and GTC packs are very good, the BTCC cars by Patric Marek, the Caterhams on RD by Ben and quite a few others...
Good luck and looking forward to seeing your app grow