Thing is, there is no shortage of things to buy in CoC and even more things to buy in the Revamp. What I was referring to when I stated "money sinks" is something continuous. A donation box idea is a good one, so long as it doesn't terminate its use at some point.
Maybe if there were illnesses, infections, or diseases that could only be cured or remedied with consumables (e.i., sleeping doesn't fully cure) and can be brought upon the char at anytime, early or late game, from level 1 to max cap, and adversely impact the char in someways that leave little incentive to simply ignore them. I know SSTD's, or what ever they are being dubbed, were planned for TiTS and sounded a lot like that sort of thing. It wouldn't be hard to have it make sense, even the player character can catch a cold sometimes and needs a day off. You could add a tolerance level of sorts, like an immune system, in order to make it progressively less debilitating for higher level characters, and then restrict the most troublesome ailments ones to sources only higher level characters should be for to balance the effects and keep them from being too much of a killer. Lack of sleep could adversely undermine that immune system. Maybe the effects are mild or even passable at first, then slowly become potentially lethal for some of them. That could make it imperative to deal with, just not immediately dire or fatal. I don't know about you guys, but by the time I generally hit 20 something in level, I can hardly find anything worth while to spend money on unless I need it for something really specific and many of those items have sources that don't require gems. Something that creates a consistent demand for something even if case by case is relatively cheap and affordable, rather than to simply be really expensive but once-and-done, could help make end game a little more dynamic and interesting. Sounds familiar actually...like hunger, huh? Could be a good addition to that mechanic. It'd be a lot of work, but pretty nifty and could even be inclusive of hunger.
Eh, I need less Red Bull in my life apparently...or more sleep. Probably both.