Well AOW is definately better and worse than MOM.
Better in that it has far far fewer bugs, updated graphics, and both hotseat and internet multiplayer (a huge plus). The siege battles are also incredible and I really like the hall of enchantment and tower thing that shoots at people.
Worse in as you say the heroes aren't quite as distinct, and there are a few less spells and more importantly less spell variety. (I miss phantom warriors and summon island alot). I'm not sure I quite agree about the unit variety though, or at least it isn't as noticeable as the spell/hero variety.
I'm rooting for a new MOM for sure, but I don't think stardock is up to it really, just going by the quality of their other products.
My prof. actually worked on MOM 2 before it got cancelled. It was going to be an RTS crazy enough.