I'm not as concerned with being cooked as I am with air quality. I know there's been some activity in the last few years, would it be a good idea to make room for a simple respirator in my first ait kit?

No, unless your climbing an active Volcano.

I climbed both Sabancaya and Ubinas last year, there were some fumes at the top but nothing that caused us any problems. Check my trip reports if you would like to see photos. Even Misti has fumes if you go down to the crater, but again no problem. Now going into the craters would be a different story! Vic