I usually buy 1-2 at a time, and my buying sprees happen at one of two times. Either one of the boutique manufacturers who I like releases something I find even the slightest bit interesting and I pounce on it to try it (MVP's speed 7 fairway drivers for instance) or one of the main players releases something that I think will fill a slot in my bag (Buzzz OS).
My disc buying history is probably not that unusual. Beginning in the early 2000's I played in college as a 1-3 disc wonder, and enjoyed the game thoroughly. I only played one course, so an Eagle, Spider, and JK Aviar were all I needed, although I did buy a few extra discs when I was feeling flush with cash. I bought only Innova because their flight ratings made more sense than Discraft's, and their plastic looked nicer. After college I quit playing for many years.
When I got back into the game a few years ago I found a local disc golf store and this site and realized how many options there were. Back when I was in college it was only Innova and Discraft (at least in Bowling Green Ohio) and as I said I didn't throw Discraft. In college I was choosing between buying a disc and buying beer for the weekend. Now I'm choosing between buying a few discs and cooking at home, or going out for a nice steak somewhere. My point is that the consequences of a disc buying mistake were and are significantly reduced, which left me the option to try out Westside, Legacy, Discraft, MVP, Vibram, Lat 64, Failent and Gateway. I went through a period where I was buying 1-2 discs a week, and giving up on discs before really learning them.
Now I've found a fairly stable mixed bag. Roughly half of the MFG's listed above have a place in there. At this point I'm kind of getting back to my college mindset of only buying from certain MFG's because I can compare a Volt to an Amp, or a VP to a Sole and know what I'm getting. I'm not saying I won't give others a try, but it is going to be harder to find a spot in the bag for new discs, so now I buy less. As others have said, mainly backups and or cool colors to dye.