Active Merit sources can't make up for inactive sources, so the inactive users should be replaced.
For what? So that new merit sources to the same users throw their merit? The current sources have already raised the rates for evaluating posts, it is already rare that anyone throws 1 merit per post, at least 2, 4, or even more. What problems will new merit sources solve? None.
It makes no sense to change inactive sources to active ones so that they just exist.
New merit sources should give preference to the good quality posts no matter who made it, if Theymos made any changes in the merit sources lists. Even if theymos is not interested in adding new sources, its better to reallocate some since some merit sources have very few smerits to spend from their source which was even less than 100 for some.
Your first point about quality can be subjective or objective, so source members are going to come to very differing conclusions about those kinds of matters, and I doubt that theymos would have any problems with that and the standard does seem to be more concerned with either potential abuse or even being inactive.. but lots of latitude seems to be allowed in determining posts/members to merit. .. .so in other words, findingnemo, if theymos wants to consider your merit distribution philosophy, he may well either add you (or your type of a member) as a source or increase your smerits if you already are a source, to the extent that theymos even wants to do any incremental changes to what is already happening.
I do agree with you that there does seem to be a number of merit sources who have decently (or would it be relatively) small source allocations, and of course, relative to a non merit source member, anything might seem like a lot, but relative to some other members, it may seem like a little.. 100 is actually not a bad quantity.. and even 50 or 60, which would still be 2 source merits per day.. so sure, it might be difficult to know or to hypothesize if tweaking a few members might be helpful or if theymos might be considering that if he does it, then he is going to do something BIGGER.. (so speculating again, regarding what theymos might be thinking in terms of tweaking, big changes or even total overhall - which would also be potentially scarie, until it were to actually happen and we know what we would be dealing with - under such a total overhall scenario, were it to occur).