This is a personal preference thing. If you like your MTB stuff, use it. At least for a while.

As for Speedplays, I have them and love them. I have yet to step in anything so bad that I could not clip in. If you are worried about that, they make covers that snap on for when you feel inclined to go hiking through mud, dirt, and snow. For me, the benefits of Speedplay more than make up for any drawbacks the cleats may have.