Yes, I agree with ogden in the idea that if the firmware for the "node" is really super simple enough, it's fine to prototype the software once and then mass program.
If it's <100 lines, configuring ADC and SPI, or possibly bitbanging a simple control interface, then chances that there is a hard-to-find, hidden bug left after initial development is small. It's nonzero, but you can take the controlled risk.
I have been pushing my luck to >1000 lines of code, more complex distributed designs and have been quite succesful, but yeah, I understand it's a bit scary.
But if a cheap SPI ADC does the job, I wouldn't go this way just to save some cents; the price difference isn't that much. OTOH, if the SPI ADC doesn't somehow produce the wanted datastream format, for any reason, then an MCU replacement quickly becomes attractive.
Those On-Time-Programmable cheap Chinese controllers would be spot-on. Yes, there is a risk, but also learning opportunities.