I only have two cars but I have multiple models set for each car and I've set the radio up for in terms of car feel/track conditions. I usually label them something like 2WD Slick, 2WD Clay, 4WD Clay, 4WD Slick, loamy whatever words work for you, etc. It seems a lot of guys don't adjust their radios much so this may not be very helpful for them but I always tell people they should try it. A little Expo on the radio is much easier to mess around with rather than adjusting the car suspension/gearing/ESC settings. That being said I also use my ESC settings often to adjust my power band for the track. I find steering expo to be very helpful when you just wanna dial a touch of that tweakyness out right before your heat starts.

Also, I have been running Low Self Discharge NiMH batteries in my transmitter and I charge them every couple of months or longer it seems. I don't race often but my radio is ready to go after sitting for 3-4 weeks. I wouldn't run a LiPo in my transmitter for fear of puffing and I would also expect it wouldn't hold a charge as long while sitting in my radio bag for a few weeks. I also like being able to grab AA's anywhere and make it work. 7-11 has AA batteries!