Dumb question(s): Is it possible to do "traditional" HF/VHF ham stuff with these mini SDRs? Is there a good software package that emulates the old-school rigs (but with fancy new features)? Are these radios powerful enough to drive an amp to get to something like 100W (or 1500W) on HF?
You're probably not saving any money this way, but you do learn a lot.
Those mini SDRs when used for transmission will output a ton of harmonics because they are almost by definition not going to have any filtering on their output because that would limit their usability. When used for reception that is not a problem, if you start using them for transmission it's a completely different matter.
Keep in mind that a power stage that responds well to a particular signal absent filtering is going to respond quite well to the main harmonics too!
Anyway, I think you can send signals in baseband from the computer or the SDR and let the radio modulate it.
I hand build a few of the early prototypes and have a couple of the production versions too. I cannot emphasize how underrepresented I think this radio is compared to a lot of the other SDR hardware out there. It compares favorably in performance and vastly exceeds the features of most amateur radio HF transceivers in the <= $2500 range.
Because it speaks the OpenHPSDR protocol it can also run a digital predistortion algorithm called PureSignal that samples the PA output and distorts the input signal to correct for amplifier phase and power nonlinearity. Digital predistortion is relatively common in modern radios like cellular baseband, but to my knowledge PureSignal is the only open source implementation of such and the only implementation publicly available for an HF radio.