I agree, yes it is only one person coding and cannot be compared to the 100s of people that do just the sounds of another game. In terms of racing games out there right now LFS is up there with the other games because LFS does not play engine sounds from sound files but like IRL the sounds comes from how much pressure you apply the the gas pedal, ETC. that is why the sounds are kind of boring, but you really couldn't expect too much from that type of sound.
But that cannot be an excuse not to get better, the suggestion of hiring a new person is a pretty good idea, thinl about it, 3ppl = LFS(amazing game), now with twice that number what will we be expiriencing? I'm sure there are lots of skilled people out there that are willing to help out.
The sounds are important and I do feel that LFS is lacking some things, the most important is shifting sounds, I don't know how you could hear them, I could not, I have used many different kind of speakers including the normal pc speakers home stereo ones, stereo headphones, mp3 headphones, and I can still tell that there are specific sounds missing.
I think that in the upcoming stages S2 will get even better than what it is now, we'll just have to wait and see, and was 2 years of wait for S2 worth it? I'd say yes. Plus if you compared the first alpha of S1 and the finished S1 product you can tell that S2 is just going to get better.
So my point is that sound is very important, and I'm sure improving it will make the game much better,