I can't count any more PMs coming in for me.
I have just the opposite experience, no one has ever asked me for any service related to merit - neither to give them away, nor to sell them. Maybe the thing is that those who do it target merit sources or have some other criteria that my profile doesn't meet
It's very hard for an average poster to rise through the ranks, hell, even a decent poster probably won't achieve the sufficient merit to become a Hero within the timeframe it takes to get the required activity so skipping the queue by donating seems like a win-win to me.
Maybe then it's time to modify the current requirements, which are obviously too difficult for most new and some old members. If 1000 merits is the current request for Legendary rank, maybe we should lower it to 750, and Hero from 500 to maybe 350 or 400 merits. Of course, the question arises what to do with lower ranks, because in my opinion Jr. Member is very easy to reach, just like Member (1 - 10 merits) but even 10 times more is needed for Full Member rank which is too much in my opinion.