Yeah but why are his mtn shoes worn out? Possibly because the OP used them a lot more often because they were better.

If the OP is going to be riding dirt roads, I'd suggest going with a mountain pedal, because my experience with Speedplays is that the cleat can get gunked up and not clip in and out right if it gets any dirt in it. The old ones would get gunked up literally by walking across dry grass, the newer ones are better but nowhere near as good as mountain bike cleats that are specifically designed to get dirty and still clip in and out.

My 2 cents.