Honestly, without a specific project in mind, I'm not so sure a DSP controller is a good way to learn DSP.
There's plenty of software for simulation, and books on theory. You'll be able to see all the important things like a FIR's response and FFT's results with simulation, but that's hard to observe accurately and comprehensively with a hardware part here.
There's a lot to how to apply DSP to a hardware system once you KNOW DSP, but that's actually far less than understanding DSP itself.