Thanks for the help so far, guys. I'm working on the spinning. As for the nutrition -- well, that's gonna be a slow road.

I just got back from another 30 mi trip (I follow this bike trail that 15 mi long each way).

After this ride, I have a few more questions.

First of all, I'm having a lot of trouble clipping out of wellgo pedals on my bike. I asked the guys at the LBS about them and he mentioned that it might be my shoes, because I'm using mtn biking shoes. Do shoes make a great difference (mountain vs road) or should I switch the pedals first?
I saw another guy clipping out of Look pedals which seemed remarkably easy - as for me, I have to unclip way ahead of time before a stop for fear of getting stuck (learned the hard way after a couple falls).

Also, after about thirty miles, I find that my bottom begins to bother me as well as my lower back. I had just switched to a Selle Italia Flite Gel saddle but don't seem to notice a great difference in comfort. I also suspect my saddle is a little low despite having been fitted at the LBS, possibly leading to a little lower back discomfort. Any suggestions?
I'm wearing a $40 pair of Pearl Izumi bike shorts. And I'm a pretty thin guy (not much natural padding). Think it would be worth it for me to take the dive for a more expensive pair of bike shorts? UncaStuart did mention that the $80-110 variety were "like buttah." But I've heard other comments to the contrary.

Nevertheless, despite little issues, I must say that I find I'm always itching to get on my bike whenever I have a few free hours. Thanks for all the advice!