Nice thoughtful post! I think both ideas are worthy of discussion.
I've said before that maybe we fork to n^x curve where the witnesses adjust x like they now adjust SBD interest rate. x is currently 2 but could be 1.1 or 1.5 or whatever seems to work the best, and can be changed by witnesses without another fork. Of course the witnesses have to be trusted to be able to choose x properly, and some think they aren't that good at choosing the SBD interest rate; I have received that as a counter argument.
Gamification is interesting. There is an argument against holding SBD as it is debt and hinders the rise of Steem price. Not sure if giving more SBD as interest is good but I am open to it. Getting more SP here on steemit is an incentive in itself due to higher curation rewards. Maybe just the display of a level, based on your SP holdings, would be incentive enough. People love to show badges and move up leaderboards, so sometimes just the display of number and position is gamification enough. But I'm open to other ideas!