The particularly tricky thing with balancing is going to be for things (and rares are probably in this category but not the only thing) where there's a very efficient way to do it but most people aren't. And another thing is where multiple activities can be combined: you're not likely to get a decent merit rate just doing donation missions, but you can add donation missions to just about any other activity that involves visiting stations.
For example, escape pods are something like 30 merits/tonne (depending on ethos, system type, etc.). That's comparable, per tonne, to many rares.
- in a normal system, access to escape pods is fairly limited, and this gives a decently balanced rate of return
- in particular systems, you can get many hundreds of escape pods an hour
So do escape pods get balanced to the "normal" case (which makes them superpowered in certain systems) or to the extreme case (which makes them useless in most systems)? [1] Does the balance point assume the current limpet scooping problems continue or assume you're doing Powerplay in the middle of the night when the servers are quiet and you can get it done smoothly? Does the balance point assume you're just doing escape pods, or are you also getting merits from scans, Power kills, donation missions when you dock to turn in your cargo, etc? Are they balanced around someone with a super-optimised collector ship who has been practising for weeks, or someone who's fairly new to it and just has a single 1A collector controller in their Cobra III?
And it's good if Frontier don't over-tune it, so figuring out some new technique / optimisation / combination does give an advantage.
(As I've said elsewhere the bigger question is probably not the balance between individual activities, but how undermining collectively balances out versus fortification collectively - that needs to be kept somewhat level to avoid longer-term problems)
[1] EDIT: and does it actually matter that escape pods can be obtained differentially in different systems, since they're usable as both fortifying and undermining actions? On the other hand, a fortification-only action or an undermining-only action which is very strong in a few systems and mostly weak elsewhere has different implications. Is that a problem either, though?