If it helps, here is my buying strategy.
When I photographed for a living every piece of equipment I bought was for a booked job that was going to, at the very least, cover the cost of that new gear and I saw the potential for that gear to be used again and again.
When I left the commercial field and went to art, I never bought a piece of equipment again. I actually sold quite a bit of gear. I'll admit that at that time I had more than enough gear to cover whatever shoot I might want to do.
There were of course a couple exceptions to that. Aren't there always exceptions?
My very first kit. I was going pro and I bought what I decided was the minimum needed to do the job. I also stole my dad's Leica rangefinder (that's Ok, he didn't mind

...)
Later on, when I went to editorial/commercial photography, I bought 3 strobes while I was still an assistant. I had to make the investment to work on my portfolio.
Now, are you an amateur or a pro? If a pro, follow the above rule and you'll stay financially sound.
If an amateur, well, it depends a lot on your financial situation. But before you spend money on gear that might be better spent on something more important, think hard about whether or not you really need that new gear. For example, you like to do portraits and you only have a 50mm lens. True portraits are a bit more comfortable with, let's say, a 100mm. But do you really need it. No.
Hope that helps.