If at least 3/4s of the site upgrades (such as those mentioned above) were pebble sinks, I wouldn't think that the shards would need to be limited, but since they literally require you to pay RL money if you can't play the fleamarket successfully, then that's a bit rough, especially since the price doubles every time. Like c'mon, that's really harsh.
Cook pot cost me 25, then 50 moonstones to upgrade – my next upgrade will cost me 100 moonstones. That totals 175 moonstones, which equates to almost $20 USD (which, in my local currency, is almost twice that!) amount; and the same amount is required for mining… Add in the other Moonstone required upgrades, and you're creeping into high RL money drops. Now, $10 or $20 purcahses might not be a lot in the scheme of things, and I understand that the game needs to be supported by Players buying moonstones and whatnot, but I really don't feel like we should have to fork out IRL $ to get basic gameplay happening – and maxing out the cooking pot, and the den is honestly basic gameplay.
Customs, recolours, genes and even apparel slots I can accept being moonstones, because they're not required to make the most of the game. You need to mine to create stuff for your pack; you need to cook to feed everyone efficiently; you need a decent-sized den in order to ultimately partake in a lot of activities (Hunting, campaigning, and gauntlet will all be more effectively played with a wider variety of wolves to pick from for example). I don't really like having to pay moonstones for den tabs, but like apparel, they aren't required to play the game, just to make it prettier.
So yeah; the majority of game upgrades should either be pebble sinks, or the cap on moonshards needs to be a lot higher/non-existent, so that those of us that can't drop much or even any RL$ into the game, can still feel like we can fully enjoy it!