Ok I'm just thinking out loud here:
So the Beaglebone Black is a nice little package and there seems to be a lot of support for it out in the wild. However, it can really only DO a few things at a time before the single core CPU gets swamped. It's possible that someone could 'cluster' them but I don't think it would be as efficient as using something like a QUAD-CORE board like the ODROID-XU3 or a Adapteva Parallella-16 (16-CORE).
I suspect that my "Driveby" application may end up running on two boards networked together. One Odriod-XU3 as a storage device/webserver/mobile-desktop (since it has more ram than the Parallella has) and One Parallella-16 to connect to the RTL Dongles AND a HackRF (perhaps).
One interesting aspect to the Parallella-16 is that is has access to an onboard FPGA. A pretty decent one at that!
The shame in both of these is their limited/fixed Ram 2Gb on the Odriod and 1Gb on the Parallella. Not expandable on the boards.
Both boards are fairly cheap at between $150 and $180 minus accessories. And considering that some of these are faster than low end laptops that's pretty cool! Not to mention most of them draw about the same power as a cellphone (or less!).
Anyway....I'll continue with the Beaglebone Black for now. I have a second unused one on hand that I could network together with the one I've been using to ease CPU swamping. However I just don't really like the idea of having to do that at this point so I may just hold off until I can find something like the boards I've mentioned in the post OR possibly something even more exciting in the near future!
It is truly a good time to be involved in computing as there is a new surge to produce highly optimized low power, high performance computer devices these day.