If the cost and complexity of installing a paint booth that size were considerably less than has been estimated, I wouldn’t have any objections, but then if that were the case, we wouldn’t be having this discussion- we’d just do both upgrades. Unfortunately, it’s not as cheap as the old paint room stood to be, and either way it’s going to cost a significant amount, to add function that can frankly be accomplished at home with newspaper, cardboard, or cheap plastic sheeting. It’s not like having an operational plasma cutter (which we really don’t have, even if we had ventilation). I mean, I can paint in pretty much any location outside of my house, and I’d imagine so can pretty much every MakerSpace member, but my access to a plasma cutter is markedly limited under most circumstances.
Regarding the very-large-tent booth idea, I did paint a car under a 26 foot canopy in my driveway once. It actually came out pretty decently, except for a considerable amount of trash that got into the paint because it turns out you can’t really control airflow using only a tarpaulin canopy, plastic sheeting, and a pair of box fans. (One of which burned out during the affair) Even if it didn’t put us in regulatory trouble, it’s just not possible to control airflow or humidity well enough in that kind of circumstance to make such large projects feasible. I’d probably paint a car under the canopy again, if only because the whole setup cost me $400 and I still have it all. (Though, I’d definitely invest in tarp for the walls, rather than plastic sheeting.)