ditto Liza and aicabsolut.

I also agree that walking on road shoes isn't the end of the world. In fact, the last time I rode in the NC mountains, I had to push my bike up a steep grade for about 1/2 a mile in my road shoes. It's survivable.

Like you, I used to have hot spot problems when I started riding distances greater than 35-40 miles in my MTB shoes on my road bike. I have bad feet, so I needed the larger platform and a stiffer sole. I still use those same MTB shoes (Specialized) for all day mountain biking or touring, but for long road rides, I have Specialized road shoes and the SPD-SL cleats (the Look type) and they totally solved the hot spot issue for me. (I do have to order online though - I wear tiny mens shoes - so no local store ever carries my size)