Tyler has made a few posts about how better camera gear makes for better realization of the things you want to create, in this case, photographs. He has a friend discovering that good glass and a full-frame body remove all kinds of limitations, and he experienced that himself when he had my Canon 5D for a couple of months prior to shooting our wedding. Indeed, when I first got the 5D and took it to Walt Disney World, it was like I was shooting for the first time again.
When it comes to photography, this scenario causes you to gain sharpness, resolution, greater control of depth of field, wider angles and lower light shots with less noise, among other things. There's a cost associated with the gear, unfortunately, and few things are as frustrating as financial constraints when it comes to feeding your passions.
I'm the worst when it comes to this sort of thing. In 2006, I bought Panasonic's first shot at bringing professional HD to the mid-market, at a cost of around $7k at the time (plus three or four more in accessories since). I had potential freelance work that I eventually did land, and made back more than half of it, but even with the remaining amounts, I've had the chance to create the quality of video I did when it was my primary job function. That pleases me.
A little over three years ago, I also stopped buying computers on the cheap, since I was more or less throwing them away in a couple of years or having to upgrade them. Since these are the tools of my trade, I now realize that getting something more solid is worth the expense, considering how much I use them.
Some people buy a hundred pairs of shoes in a year. Other people load up on DVD's. I don't think that buying tools that help you create other things is in the same category, and as such, shouldn't suffer from the pre-purchase regret and guilt.