I always delay buying things, unless it's something I urgently need. By waiting, you not only are making sure that you really want it, but are also giving yourself time to learn more about it (eg, you keep hearing friends talk about their smartphones, so you can assimilate information about which models or brands are best before buying).
In terms of drumming, you say "if I continue drumming". If you are not sure that you will continue, then I say buy the cheapest set you can (within reason!). If it gets worn out because you are drumming so much, then you know it would be best to invest in a good set that will last longer. If they break altogether but you are still drumming, then you can count that as a "need" to buy new and better drums!
In terms of technology, it is always best to wait. If you have your sights on a particular model and wait until the new model comes out, then you are getting the model you wanted for less than you would have paid when it was new. I had been thinking for some time before getting my first smartphone. My old phone was on its last legs, and I knew I wanted the new technology. But I put off buying one, and eventually a friend was selling a good model secondhand, much below its retail value. Had I not waited, I would not have found the good bargain. Same thing happened when I was thinking of getting a car (which was not a need for me).
Impulsive buys generally mean you spend more, and may mean you end up with something you are not really happy with or feel you shouldn't have bought at all. Many times I've been convinced I wanted something (usually a cool piece of clothing) but waited awhile and eventually got over wanting it, which shows it wouldn't have been a particular good purchase.
Even in terms of pets: I've always had a better time with animals I came across "by chance" and adopted, than pets I've decided I wanted and went out and bought.
So I think, as others have said, that delay is best. When your "need" becomes stronger over time or your desire doesn't fade, that is the time to buy.