It's hit or miss. Me, I go for all the detail. Others, just for speed. I have mirrors on my cars, others don't even put the headlight buckets in behind the lenses in an effort to save that microgram. (My upcoming SRs will not have the exterior mirrors, but will still be fully detailed otherwise). A lot of guys are using Funny Car bodies

, so there's not much detail to be had.
A side by side of two Lamborghinis in different levels of detail at the March NPWDRL race (at the 55s mark). The white one is 1:24 scale, green 1:25.
(I should not have sent in the green Lambo as the rear wheel was fouled)
A Skill 1 (Snap-Tite) kit will use thicker (read: heavier) plastics throughout — so you'll have less ability to add weight where you want it. A Skill 3 or 4 may have more details that require more skill to mount (like lining up the rear spoiler on a Viper ACR).
A "streetside" model (like AMT's Showroom Replicas series) don't have opening hoods, so that's one fewer fiddly bit to deal with.
Other than that, though, the world is your oyster (as long as that oyster is <= 8.25" long).
Feel free to hit me up with any questions. I ain't fast (yet), but my cars do look good.