S2 is worth it because it will last a year or more until S3 comes out (only estimate of time before it comes out). The only reason there is not many servers in use right now is because it is the lowest peak hours for LFS drivers racing online. The game is much more popular in Europe and Australia, and North America is stuck right in between their "sleep" or "busy" times when they aren't playing. This is usually the time the play volume is very low.
In about a few hours or so, the amount of people playing online will rocket up and there is plenty of people to play with. So if you are in North America, to get the most choices for playing online, you'd have to play during late afternoon / early evening, or very late evening / early morning.
It's not that bad, and I wouldn't let that be the reason why not to buy S2. On weekends you get even more people playing.
This here is the current activity chart of LFSW (usually shown randomly at the top of this forum)
You can see how high it peaks.