It pretty much has to be a firm decision on your part to slow down in one way or another. When I got "hooked" a number of years ago, I reached a point after a year or two where I decided that I would take a period of six months or so and see what lights I actually used and wanted/needed, and start selling off the rest. At one time or another I had much of the Surefire line:M6 (3 of them), M4, M3T, M3, M2, 12PM (x2), 9P, 6P, L6, L5, L4, L2, L1, A2, E2e, E2D, E1e, E2W, E1L and probably a few more I'm forgetting, as well as several ARC LS's, AAA's, some SL's, a bunch of cheaper lights and a few custom lights. Not as bad as some on here, but way more than I "needed" or used on a regular basis. After evaluating what I needed and actually used with a few extra thrown in for the cool factor, I ended up selling about 2/3 of my collection and brought in over $2000 IIRC.
I kept the SF M4, A2, L1, E2e, E1L, 6P (w/A19), G2, a Tigerlight, SL Strion & Poly Stinger, a couple of ARC AAA's, Fenix P1, and some mildly modded Mags along with some of the cheaper lights. I still buy several new lights every year, but typically only spend $100-150 a year at most on new lights instead of thousands of dollars a year. I picked up a MagLed 2xAA a few weeks ago, and have my eye on a Fenix P1 CE, but no longer feel the need to buy every new light that comes out. I keep several in each car, use a few in my garage, and have several that I EDC. There are worse things a person can spend money on, but it isn't hard to get out of control.