It provides a metric of their opinions. Or do you mean this in a sense where advertising is already the status quo? What are we worried about on nostr? Relays being ad supported? I consider any communication with what I write some amount of value. Even if it isn't monetary.
“A metric of their opinions” to what end? Does that give you some kind of emotional validation of your worth as a creator? And yes, you ought to be concerned about relays and clients becoming ad supported, because advertisers wield a lot of influence. When clients or relays become ad supported, you (the end user) are no longer their customer. The advertisers are now their customers, and that will greatly impact their decisions.