The problem with a gradual taper is it creates a clear incentive for people to create multiple accounts.

You'll still have your hill :) You just have a point to reach where you will be at the 'top'. You will also get a lot more reward for actually getting there.

Try to look at it from the perspective of a mainstream users. I know you and I don't have a big issue with putting in a ton of work for very small incremental gain, but it is a big turn-off to the platform for the majority of users.