The physics and graphics engines are common across all licence levels, from Demo to (eventually) S3.
S3 is not going to be a mandatory upgrade. If you don't think it's worth it for 1 track and 1 car (as far as we know, all that S3 brings extra to the table), then I really think you shouldn't buy it. Nobody should make a purchase they think they may regret and I'll fight your corner for you if you decide not to upgrade, and then cop any crap for that decision.
[edit] sorry geeman1, dunno why your post didn't show up before.
ill jus tbuy s3 so i can race on any server with any car nothing more id hate then to have a server i click on and say i cant join as i dont have content. i want it all. in support of lfs xD
Well Mysho you may as well try iRacing as well as LFS as they only have real tracks & real cars. $5 for a trial is pretty reasonable. (dont get sucked in tho everything else is very expensive)
Who says stock cars cant be driven on road courses? Besides it would make both ovals more interesting and it'll be more than just plant your foot down (try the I-SCAR mod to fully understand what i'm talking about)
Stock Cars have also gained a new meaning in motorsports. It also means racing of a purpose built car that is heavily regulated through chassis and engine. I mean the SuperLeague Formula is billed as a "stock" formula but that doesn't make sense in the "traditional" sense of the word.