I've only been playing LFS for less than a year, so I guess I don't even qualify to answer this question. But part of what's been keeping LFS "fresh" for me is all the new gadgets that I've gotten; multiple brake mods, FreeTrack +++. Each of them adds a little more to the immersion, which makes LFS closer to living out its true potential.
And best of all, some of these mods are very cheap or even free. Try it out! Can't hurt. (Check out the FreeTrack thread in the Other Hardware forum for starters!)