I really like your idea.
Under current rules more and more people will start saving all their votes for themselves, ignoring engagement with others.
If I understand it right, in your system you power up your vote by voting on people. Then, you can spend your high power vote on whoever you want, including yourself. But you had to at least vote other people along the way (meaning: actually ENGAGE the platform). Not bad... not bad at all.
That's not really what I meant - you don't gain voting power, it's just that it reduces slowly up to a certain point. Personally, I quite like your idea, but the problem is abusers will be more incentivized to keep voting on their own spam :)