I use a USB wireless adapter, and I do fine. I've only ever been told I was lagging once, and that was because I'd accidentally left Napster downloading in the background. Granted, I race mostly TBO, but I can still race close to other people, and when I save an .SPR, I don't appear to fly everywhere on the track.
Most people aren't in the same situation as you, Becky, where they have a choice between wired and wireless, and I don't see the need to restrict people's use of LFS because of that.
P.S. I'm directly above my access point, and I get 90-100% signal strength all the time, but I need a 60 foot ethernet cable to get to my router, because it needs to go down the stairs, so it's doable but very inconvenient.
P.P.S. A slow computer causes more lag than a wireless internet connection.