I'll grant Lewis has a great ceiling, but man, that floor....
Martin hit at AA in his first full season in pro ball, Lewis hasn't hit that well at any level, has he?
IMO, Martin is a at least 2-3 WAR player in his ok years, and a 3-4 WAR player for at least several years. You better be 100% right when you trade him, because that's a good MLB player.