Many of us have that one game where we will buy expansion after expansion, miniature after miniature, new booster pack after new booster pack, etc. no matter what the publisher releases. Family, friends, significant others may sit and scoff or wonder why you're doing what you're doing. For us, it's enjoyable. There's a game in the chase of completion. This behavior is most prevalent in Magic the Gathering players, or really any CCG, but it also shows up in miniatures gamers, and yes, even boardgamers. Heck, it shows up all the time within many video games. Pokemon magnified it with "Gotta Catch 'Em All" and by gum, we do. We have to keep going until we have everything and nothing will stop us.
Personally, I've had several versions of this over my life. I started out with the Star Trek CCG in 2nd grade and that lasted for a few years. Pokemon (game and cards) came around in 5th grade and lasted for 2 years. At least with Pokemon I managed to sell off my cards, and I haven't played a game since Silver/Gold, though that is going to change in October. Somehow I managed not to have a compulsion during Jr. High and High School, which was good. College saw me get back into Star Trek CCG, and then came boardgames. Well, I've been fairly good about not having a completionist mentality, but for awhile I bought everything Carcassonne, then everything base Munchkin, everything Dominion (which is still going on), everything Small World, Formula D, etc. And that brings me to my current sink, X-Wing. I'm helped by the fact that there is no randomization, which is really useful, and one of the main reasons I'm sticking with the game. I will never have a "complete" X-Wing collection. Sure, I can have 1 or 2 or 3 or more of everything, but there will always be room for more, or maybe not.
So while I have a money sink, perhaps more than one, at least it's a controlled sink. I'm not out chasing 40+ unique "rare" cards where you only get 1 per pack. I'm not trying to collect countless Heroclix figures. I'm not buying multiple booster boxes for the new set of a card game every few months. I'm not buying a new chapter pack for a LCG every month. Even if I was buying those things, it would be ok. There's nothing wrong with those pursuits, so long as you're enjoying them and you're getting a return on your investment.
What I'm getting at is we all have that one aspect of our greater gaming life where we're going to invest money. Some may see it as a waste, but we enjoy it. As long as you're paying the bills and taking care of yourself and those you are in charge of caring for, it's ok to use your discretionary spending on something you enjoy. After all, we play games (card, miniatures, board, etc.) to have fun. We collect things to have fun. Being able to merge those two is a great thing that results in a lot of fun.