Maybe a choice when you power up, you can get a fixed interest rate but you don't get curation rewards and is slightly less roi than curation as you have to.put the effort in, no interest rate but you can curate and maybe a third option where you can choose/split how much stake you want for a fixed return and curation.

Maybe make downvoting only affect your rep? And make it not stake weighted so one downvote only equals 1 vote rather than a big staker putting off someone. Would show the majority view of someone's rep as its misleading if one big staker can influence it that much.

I also like the idea of an increasing roi based on how long you have powered up for, maybe have the option to have the roi be made liquid rather than powered up, prevents people doing big power downs and having a negative affect on other users.