I've had the WM Hooded Aspen for four years now and just love it. It has become my PCT bag of choice.
You're right about the convenience of unzipping it completely to make a quilt, although it's kind of big for one person that way. If you sleep in a floored shelter, that's no big deal, but without a larg ground sheet, you risk getting the inside liner of the bag in the dirt when used as a one person quilt.
The fact that it has two zippers - one down the side and another across the foot gives you a huge array of venting options. I like to leave the foot completely open and if I get too warm, a little bellows action draws cool air through the bag.
Hooded vs. no hood - your call. Personally I prefer the hood because my shoulders get cold easily. Also, I don't have to carry the extra balaclava and hat that I'll need when it gets cold.
Bottom line - well worth the investment, and WM's quality is solid gold.