I believe users, except for merit sources, aren't very interested or don't have much time to spend their merits.
~
Users need to spend their smerits as well to achieve the ranks.
If you're forcing someone to do something he isn't interested in, it's probably not going to be this:
I encourage people to give merit to posts that are objectively high-quality, not just posts that you agree with.
Another idea is to get back merit rewards. Like spending 2 merits, the receiver will get 1 spendable merit. And the sender will get back 1 merit to their profile. And both should be spendable merits.
If you mean sending 2 Merits creates 2 new sMerits, you'll end up with infinite Merit being created. The current 50% is fine: that means each sMerit from a source can create a total of (almost) 1 sMerit down the line, and it stops there.