You are absolutely right that you can do virtually everything with a spinning reel. I used to use Daiwa 3500 series reels for years before I got into baitcasters. Weight becomes more of a factor as the day wears on. The 3500 weighs approx. 13 oz. compared to a Curado (05 and earlier) at 8.5 oz. That really starts to make a difference after 7-8 hours of pitchin' into the brush. For me, the wrist position when holding a BC is less fatiguing than when holding a spinner. You are also correct about the rod being the primary "power" used to move a fish while the reel simply retrieves the line. However, there are those instances when it is really to an anglers benefit to be able to crank hard on the reel while pulling the fish with the rod. I learned this while fishing for Yellowtail around kelp patties. Yellowtail are nitro-charged torpedos that make a bee-line for whatever cover they can find when hooked. If you hook a decent 'tail near a kelp patty you either hunker down the drag and crank/pull the beast away from the patty or watch your line go zigging into the mess...from where no hook returns. Perhaps this is a bit much for most bass fishing situations but I have personally lost fish that I feel I could have landed had I been using a BC instead of a lighter spinning reel.

I'm not trying to sound like a know-it-all here, I just really think that it is advantageous to use baitcasters in certain situations.