i think modding is an excellent idea. i think that some servers should allow or disable car modding usage for clients, in case some people dont like the idea. just imagine someone pulling up beside your BMW M3 in their Porsche in a San Francisco city track. you look over and see him revving his engine. the light turns green and you race him down the road and onto a busy highway of other people in their cars. what happens next? yep, youre right! in and out they weave through traffic and continue down a long stretch. but then, the inevitable happens: a cop in his lamborghini chases them down the freeway and onto civilian roads. but the superior performance of the lamborghini's v12 overpowers both of them and theyre busted.
or if youre not much of a street racer, there are other benefits available with modding. more variety in the cars allows people to simulate real life situations in which not everyone has the same car. race down aston in your ferrari f430 with the top down against another person in his lamborghini gallardo. this is a fair match and the allowed cars should be chosen by the host in order to achieve a fair race.
also, there should be a filter that prevents some noob who somehow knows how to mod from making a block car with 1000 horsepower with a top speed of 500 miles per hour. for example, there can be a limit of lets say 500 horsepower and 200 mph, depending on the type of car. if this doesnt work, you can just require that the mod is sent to the developers for approval and insertion into the lfs database of cars (much like the lfs skins on lfs world) so that they are visible to all racers.
hows that?