This is the part where you realize you don't have enough time to play ALL the awesome games that come out every single week(or days in some cases).There always is a gem which you "have" to play just to see why is it so good.
However I'd advise making a list and notes as to which games you've heard and once you want to play them when they're on a deal,just buy and play it without looking back at anything else.This way you can save a lot more money,because you'll be fully enjoying each product you buy instead of most just sitting in your Steam library,waiting to be "played at some time".
Also here are some awesome sites where you can also get bargains:
GOG.com [http://www.gog.com/]
Green Man Gaming [http://www.greenmangaming.com/]
GamersGate [http://www.gamersgate.com/]
Last,but not least,help making interesting projects develop and be released for all of us to enjoy:
Kickstarter [http://www.kickstarter.com/]
But remember,your limit isn't money,it's time,use it wisely,especially when you know a game is going to hook you into playing it for quite a while.Don't buy every game on a 60% and below sale,don't buy every good game you hear,buy a good game on sale which you are going to play at the moment and your hobby won't become as redundant.