I have level'd like crazy (xp, weapons, etc) with the infected roadside stuff. All have crit areas and take damage nicely. Yeah you don't get keys, but you get AS and loot you can turn in to AS, which is basically a key per 1k.
The best ones are the raider one, scan the patients one and the dark matter outpost ones. The Dark Matter ones are nice because not a lot of people cruise SF.
The raider area ones will also pick up a wandering hulker occasionally, so that is yet more xp.
I just drive around hitting those and keeping an eye open for sieges. Sieges are insane xp.

