i haven't give r8 to anyone yet. I don't compete for top 10 Squad Arena spots, but I doubt I would compete for them even after r8-ing an Arena squad because Arena just isn't a game mode I like.
So I'm just building up the mats & then if they release a new toon requiring r8, I won't have to worry about building up the mats. They'll be there for me to choose to spend if I think the new toon is worth it.
I'm not sure how many people are getting any major rewards out of bringing characters to r8. I'm sure there are some people who, for instance, take #1 in Arena where they're competing against r8 toons and they might have a hard time getting #1 without r8 themselves. But mostly r8 is an incremental thing. Going r6 to r7 yields the same amount of increase for a toon, but for many, many fewer resources.
So my thinking is that until there's a requirement for r8 for something, or until all my toons are r7, there's no point in r8.