Late to the party, but my thoughts;
I think the learning curve is much quicker on the small dinghies.
Make a mistake on a Sunfish and your going swimming. Make a mistake with sail trim etc on a C30? No big deal, the boat will take care of you. You can make tons of mistakes on a C30 and probably never even know it unless you have another boat to compare it to; racing or daysailing and somebody comes along and does a horizon job on you. "Why can't I keep up with that guy?"
Also, you learn to read the winds much better small boat and small lake sailing.
Shoreline lifts, wind shifts, puffs, etc.. you learn to read much quicker on the small boats and inland lakes.
Much of what you learn as fgar as sail trim and wind recognition does traslate to the larger boat in my opinion.
I believe that small boat sailing is the best way to learn, in fact, I recently dug my father's '75 Sunfish out from its burial grounds and I am rehabbing the little thing. Can't wait to get back into it. I have small boat fever once again.
Courtney is My Hero
If a man is to be obsessed by something, I suppose a boat is as good as anything, perhaps a bit better than most - E.B. White