Knives are a beautiful thing and are fun to have around, play with, carry, and use. However, you truly don't need 30+ and I certainly don't need as many as I have(around 16). However a few of mine are sentimental as well as favorites and others are just my favorites to carry and use.
The ones that I don't need or use or the ones that don't have some sort of sentimental value go towards other knives(I trade because I can't afford to buy most of the time). I may like them and enjoy them, but if they're seeing no use, they go, usually for something I know I'll enjoy more.
I also try to keep my number below 20, I don't need that many but I do enjoy them and often switch between several from day to day.
The farther you get into the knife thing the more you'll realize that you have formed a certain taste and you may want to stick with that, rather than have a whole bunch of knives that don't fit your personal preferences and don't get carried.
I have a specific taste that I've formed over time, and try to stick to it, that keeps my number of knives as well as purchases and trades down. =] I still get that itch sometimes but that's pretty easy to cure by doing a trade and switching things up or playing with the knives I have until I can get a new one. =]