I sail, windsurf, Kite buggy, land sail, kite board/surf, with 10+ years experience in Kite power vehicles.
IHMO, roads are not the place to take advantage of the wind. If you have a big open area like Ivanpah dried lake, or hard pack beaches, you can play with sail powered land vehicles. Small grass fields are not enough to get up to speed.
We had people show up at Ivanpah and El Mirage with sail powered wheelchairs and yes, kite and sail powered bicycles. they are mostly a curiousity, not very efficient or quick. The limited ability to resist side loading and deteriorated controlabity is the main detriment.
However, even tho it is not an effective form of transport. The dreamer, tinker and artist in each one of us must be fed. Go ahead and build it! it will be fulfilling and fun.
Meb, if you want to try kite power, drop me an IM