I've cut down on my RPG purchases a great deal of late - my only regular purchase is my Pathfinder AP subscription. I've never actually played PF (nor really likely to - the adventures don't fit very well with our gaming schedule), but still get the APs. They're interesting enough, and cheap enough, that I don't need to worry about the cost.
But, that excepted, I took the position a while back that I wouldn't buy a new game unless I actively intended to run it, and that I wouldn't buy supplements for a game unless I intended to run a full campaign using the system. There are exceptions, of course, but those are few and far between. (And since the only campaigns I've run lately have been D&D 3.5e and SWSE, that's rather limited my purchases.
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2014 does look to be quite an exceptional year in that regard - I've already pre-ordered the new Firefly RPG and the Doctor Who 50th Anniversary book, and am strongly considering both N.E.W. and O.L.D. Plus, of course, there's 5e coming out, which I'll almost certainly purchase (at least the core).
In addition to mostly enjoying reading these things in their own right, and a possible desire to support the manufacturers/my FLGS/gaming in general, I have one other argument for buying games as they appear:
I'm the sort of person that if I find myself running a game extensively will generally want to pick up the full line. This isn't so true of D&D (any edition) because there's just so much, but games like "Serenity" or SWSE (also Eberron) I've made sure to get the full line. But doing so all at once is pretty expensive, where it's easier to set aside money for one book a month. Also, most RPG books only ever get a single printing, and sometimes quite small print runs. So books can and do become unavailable - and although the likes of eBay mean pretty much anything is always available, the cost can become prohibitive (both the "Knights of the Old Republic Campaign Guide" and the D&D "Rules Cyclopedia" cost me a fairly hefty amount to acquire). So, if I have reason to believe I'll be running a particular game extensively, I'll generally pick up all the books as they appear, even if I don't have a group lined up at that exact time.
(And, since I clearly haven't meandered enough, one more reason my purchases have dropped off: I have two sets of shelves dedicated to RPGs. These are now full, and more than full. So buying more games presents a logistical problem - I don't have anywhere to put them!)
