i've had exactly the same problem. blurry interior textures in my cockpit when other cars are on the track. player vehicle at max details and opponents at high. it happend with one rf install (1 mod, 2 tracks) sharing the plr with my main install. the same mod in the other install worked as it should be, means no blurried textures.
content of the vehicle folder of the mod is also the same in both installs. only difference was the rfm file. the one in the goofy install had an entry to an non existing pacecar, which forces rfactor to load one of the mods cars as pacecar. changing it to use the hammer pacecar cured the prob.
seems to me that the detail level for the pacecar is a special one, which also affects the player car. at least on my system.
markus ;-)