The former suggestion makes the most sense to me since credits are pretty arbitrary anyways, but the idea would probably be met with some resistance from the general PrimeGrid community. Many people there have measured their overall contributions by "badges" corresponding to certain credit amounts. Also, teams and individuals compete with each other via total credit. This doesn't matter to someone like me of course, but it might matter to some.

The latter suggestion seems straightforward too. Surely the people at PrimeGrid would have thought of this already? Maybe there's some reason why they haven't implemented it yet?

Actually, there was a post by someone in their forums a few days ago suggesting similar ideas: see here. So far there's only been crickets though.