Nope no rumors of Starcraft II. I think blizzard likes to do their games right, so they don't mind waiting a while before focusing on their next project.
Starcraft I would agree has been neglected since its expansion but some would argue that their updates/balancing and differnt tournaments keeps its playablity high. Starcraft II would be a huge seller, but I'm kind of expecting Blizzard to take their time with it if they get pass any planning stages.
I don't know about Starcraft Nova but Starcraft:Ghost has been delayed for some reason or another.
http://www.blizzard.com/ghost/
Diablo on the other hand had a "semi-recent" expansion with a bunch of new options and I know that has kept a lot of people busy. My friend LOVES Diable II and goes into stories of the battles her amazon was in every so often. With the loot system, the NPC difficulty "scaling", and maps generatored on the fly, your game experiance changes each time you play. So I can see why they haven't brought up doing another game yet.