So I've recently constructed a couple of quads with the TBS Unify Nano VTX in them, and found that the level of video quality was insanely high (for analog), even when putting the signal through whole houses. Meanwhile, cheaper units that output twice the power are getting white flickers and rolling with better antennas. Am I right in assuming that some units just put out a much cleaner signal?

Exactly that. You get what you pay for. TBS know how to design and manufacture VTX's, and their VTX's are some of the best ones out there.

That's pretty helpful to know! I had assumed that they'd all generally work the same as I was under the impression that they all shared the Richwave RTC6705. Clearly that was an incomplete assessment.

Yes they are designed around the Richwave chip which simply put just handles the modulation magic but the pcb design is very important in ensuring optimal noise filtration and the signal amplifiers have a price/quality range not forgetting other components.

Ah, okay! My understanding of circuits and RF are surprisingly bad despite growing up with my nose inside of computers. Darn ICs are literally blackboxes.

Yup, not all are the same. Some of the best analog experience for me was with the rush xtv and matching cherry antennas, some of the cleanest video feeds I ever got.