Let me start by quoting my reply to your comment the first time you brought out the idea, which still remains one of my valid opinions and suggestions on this matter.
I am not talking about merit sources; I am talking about general users. They don't seem very interested in spending their merits. So it's become quite tough to earn merits for new users. I am thinking of something and recently shared Vod's thread. I am trying to think how to inspire merits senders to spend their merits.
Maybe bringing in the first suggested merit decay will be a nice idea. Let's say, for instance, if a member receives merit and tries to stack their Smerit for X period of time, it will decay in their profile if it's not spent. Maybe it will push and motivate members to be spending their Smerit regularly.
For example, to become a Hero member, a user needs to earn 500 merits. On the other hand, he also has 250 spendable merits. On the current system, even a user who doesn't spend any smerits will rank up. So we can do something on that. Users must be forced to spend their smerits as well to reach the next rank. If he/she needs 500 merits for Hero rank, he/she also needs to spend 250 merits to achieve Hero rank. I don't think it's necessary to add any additional option for user profiles since each user can see how many spendable merits they have. This is my first suggestion; if theymos think it's reasonable, he could implement it.
This suggestion looks good but at the same time is only limited to heroes once a member reaches legendary rank, which means they can continue feeling less concern over their Smerit since it doesn't contribute to their rank up anymore, or would they have gotten used to spending Smerit before then?