Do enough people use that browser to make it worthwhile?

No.

I can confirm. I earn about 2-3 BAT (€1.5 - €2) each month for nslookup.io (without serving Brave ads) and whoismyisp.org (with Brave ads) combined. That's ~1M page views across all browsers. Not lucrative at all ;)

Oh, only 50+ million monthly active users as of January 2022 - who will both earn BAT and, by default, contribute back automatically...

BAT isn't turned on by default so the number will be a lot lower than 50 million. And I expect most people to turn off auto contribution to keep the money themselves or manually contribute to sites they like.

I have. In fact, you can check this for any site using nslookup.io ;) (so meta) See the TXT records at https://www.nslookup.io/dns-records/nslookup.io