Honestly, the only reason I "want" to use my mtn bike shoes is that I can't afford another expense! I am a grad student who really should not have bought a road bike in the first place, but I did so for my own sanity. 
So I am just trying to figure out if I can get away with keeping the shoes I have.
I must say, though, that with all of your gals' excellent input, I will try out as many options as possible, and, as Wolfak says, do what's best for me. It really has been so helpful hear what several of your issues have been.
BTW, I did experience totally numb feet after a 1.5 hour ride last week, so it may well be the shoes.
Thanks, ladies!
There's only one thing better than spending a day on my bike: Spending a day on my bike in good company.