Maybe. I wouldn't be surprised, though, if the vast majority of users that you described are pretty indifferent about which photo sharing service they use, as long as there are other people they know using it. But the "power users" (I hate that term) will care about the service they use, and will influence the others. These people could be friends and family who like to follow news orgs/photographers/celebs through IG, they could be friends and family who are just enthusiastic amateurs, etc., the point is, they don't necessarily have to be celebrities or professionals that you personally follow.

So, even if you don't care about the TOS change, it could degrade your instagram experience enough that you leave. I should emphasize that this is pure speculation in an area I don't understand at all, so take it for what it's worth. And the "sucks" in my earlier comment was of course only directed at what I would want to get out of instagram and wasn't meant as a general statement.

ps, given their latest announcement, this discussion may or may not be entirely academic.

Edit: severe typo and clarification