On the other hand, I see there is a lack of merit sent out in the Mining, Altcoin, Economics or Local (Romanian - no merit sources here BTW) boards where people have real issues that need to be sorted out.
I try to merit some posts in Mining and Altcoin Mining boards but there is no way I could find time to wade through the cesspool of Alt ANNs or Economics. I don't speak Romanian either. There need to be local sources for that obviously. Other than that, if users only post in ANNs or Economics or Bitcoin Discussion AKA Shitpost Central then we can't really do much to bring merits to them. If they have something useful to contribute they need to do that where it's not drowned in garbage.
select a few merit sources that are interested in these topics and regularly posts there for a better distribution of merits
Local boards - yes. English shitposting boards - not so sure. Would there be anybody willing to do that? Should we even try to incentivize those boards at all?
have something like a "Rank-o-Thon" (similar to Hackathon 
) where a list of users would be selected and the merit sources would go to their posts and merit whatever they find good
) where a list of users would be selected and the merit sources would go to their posts and merit whatever they find goodRandom selection? No. Some sort of system that would bring attention to worthy posts might be useful but I don't have any feasible idea of how that should work. Perhaps the answer is just to add more merit sources and not expect merits on boards that have 20 threads bumped every minute by bounty hunters.