I started cycling reluctant to spend money on it, I'm usually a discounted, like a deal kind of guy. Gradually I've opened the purse strings, and at times I haven't noticed much difference, while at other times I've been blown away by the improvement for more expensive kit.
Tyres are a case in point. A lot of our club seemed to be on GP4000s. I must have tried about everything cheaper I could find. Sometimes I was plagued with punctures, sometimes they wore very quickly and sometimes they didn't grip in the wet. I moved to the 4000s and found them much better. They really appear to me to have found a sweet spot between grip and resilience.
I bought up a few when they stopped making them, and still have one left, carried in my saddlebag on an audax. I also have a set of GP5000s bought on sale at one point. I understand that they have more grip, but don't wear as well, which might not work for me.
My biggest regret with tyres is not the price of them, but that I didn't decide to pay more and try them sooner.