I think the 3-6 moonstones a day estimate thrown around in the linked thread a couple of pages ago was an overstatement. I haven't been a casual player, I spend hours and hours on this site grinding activities and professions, and within 7-8 days I've earned 13 moonstones (I may be lucky to earn another today, but I think it'll be a stretch). One and a half of premium currency a day for a lot of gameplay I'm actually fine with, it's a premium currency! But because it's so difficult to get, I'm not going to spend it frivolously.
Which of course means I'm going to focus on progression in gameplay before anything else! At this rate, unlocking just one expansion for either Cooking or Mining will take 16 days or over two weeks. Fully upgrading both will take over 8 months (if it's 25/50/100 for both, that's 350ms). If I want to sink moonstones into patterns, I'll be damaging my experience and progression with gameplay. I also can't participate in the player economy of buying wolves or custom apparel with moonstones for the same reason. I'm very quickly running out of sinks for my pebbles already though, and I'll probably have every crafting recipe/companion/apparel/wolf slot before I make my first 25 moonstones. The Flea Market for exchanging currency and buying wolves will be my only pebble sink from then on.
If it has to stay a moonstone sink, at least lower it and make subsequent costs lower (like 20/40/60 or 15/30/45) to make the time cost more manageable (11 weeks or 9 weeks) or tie it into the profession like handing over a certain amount of bars/dishes or reaching certain levels. EDITED: Math and Timing correction.