I'm suffering from USB creep and need the maximum number of hubs possible. Should I get a USB 3.0 rated hub even if my devices are not USB 3.0? In other words, does the added speed of 3.0 allow the aggregation of non v3 devices to work better?
In one word: yes.
Hubs of any kind (USB, Ethernet) are "intersections" for the connections they bring together. Your hub is the bottleneck of the "network" of USB devices. If you have five USB devices linked to your hub, they + your computer will fight for the bandwidth of ONE USB3 connection. Now, of course some devices don't require too much bandwidth like the mouse and keyboard, but some (USB HDD at copy) do.
You better have more bandwidth than less, so go with the fastest USB hub you can find.