One trick pony and swiper/slider or not, his voice, that minimalist, but insistent rhythm guitar, the weird fantastical/non-sensical lyrics and his sense of catchy melodies are hard to emulate. You hear five seconds of him - you know it's him.
I hear a little bit of T. Rex even in Prince's music, I believe the two would have gotten along well, as he matured Marc became a great friend of black music and Prince always had a heart for glam (the music, not just the outfits). Both really didn't have "singer's voices" either, yet were totally characteristic.