I'm afraid to try to add much of anything anymore and even more afraid to try to update something.
2) Browse packages by repository (mentioned before), or at least add a source repository information in package details
4) Better UI layout. Currently in 'Browse installable applications' section there are buttons with names, which is not very convenient, and I end up browsing 'All' anyway. I'd go for some kind of structured tree or such.
5) Actually, porting Smart or Synaptic as default package manager would be quite nice idea
6) Browse updated packages after refreshing repositories. Currently Managers asks me if I want to refresh app list, I tap Yes, but.. I don't really know what's new.