12VDC Fan rated at 0.08A only drawing 0.04A, can I increase current draw in order to bring the rpm up?
The .08A is most likely just a guide to power consumption, not a spec. The fan is designed to work on 12VDC, and that's what you should give it. The current draw will depend on the load on the fan which usually won't change much. You could try upping the voltage a bit but it's really pot luck how far and at some point you will damage it if you go too far.
(Of course if you have a comprehensive data sheet for the fan you might be able to learn the max voltage, but mostly this info doesn't exist on cheaper models.)
If you don't have enough air movement, the solution is a bigger and stronger fan, or multiple fans.