I use Midi and MP3 in performance. For Midi I have them loaded in my keyboards(Audya,G70 Roland, and Technics KN7000. It is true that Midi is easier to manipulate and has good sound, as long as the sound engine and Midifiles are of good quality. I also have hundreds of Midifiles on two laptops. To use a laptop, I carry a Ketron SD2 for the sound engine. It provides excellent sound but extra gear to carry. I don't Midi the Laptop to my keyboard because I lose some control of the parts I play.

MP3 and wave tracks can be loaded on my Audya and raised, lowered,slowed, or sped up with great results. I also have MP3, as well as CD&G files on my Netbook with a Presonus Audiobox. The quality of netbook audio is not good enough by itself.

Unlike you, I have no qualms mixing in Karaoke type tracks, as I need the lyrics to sing, but play the riffs.

I choose to use all tools at my disposal, as long it is evident I am much more than just a Karaoke singer.
Bernie