I focus, but my focus shifts frequently...ha ha. Like Mark, I'm going for a look. Pieces I buy need not be historicaly significant, but they need to be very well executed and visually appealling.
I have one
RULE when it comes to buying pieces for my collection: If I can't make room for it in my office either due to lack of space, or because it isn't good enough to push something else out...I don't buy it. The only exception to the rule is when I find a real bargain that can easily be flipped.
If you struggle with discipline...try my rule
I'm very disciplined when it comes to spending my money simply because I have to be. In all honesty I can say my spending could easily get out of control if I didn't have two kids a few years from college and a wife who helps me apply the breaks
I usually don't use "family" money, but my wife and kids love this stuff and my wife sees the value. So if there is an exceptional piece that is expensive I talk it over with my wife first, but am careful not to try to sell her on anything. I often sell pieces that used to be meaningfull simply to build cash reserves or to upgrade. I also use some of my bonus money from work for major purchases (slipping the misses a couple hundy doesn't hurt either...ha ha).
Here are my collecting loves:
1. Anything vintage that is 3 dimensional and related to baseball. Trophies, statues, dishes, bookends, banks, etc. I focus on pre WWII, but will add a later piece such as a nodder.
2. Pennants, but only Cubs, Tigers, and a few Yankees stay in the collection.
3. Pinbacks
4. Sporting goods advertising with nice graphics
I'll call this next section "used to love". I have quite a few of these, but don't add them to my collection unless I find a treasure at a bargain price.
1. Bats
2. Gloves
3. Balls
4. Photos
5. Jerseys