I am rarely using top equipment. It is so satisfying to see the old scrap win because of tactics, even more if you have inferior troops regarding experience. That's the game about, after all, about you as general.
I played some "realistic" campaigns though, where I simply referred to a random number generator (or if you have a dice, I don't). You know what numbers of equipment where available, so you can simply roll and buy. It relieves me from long decisions, if it is realistic to have this one. Especially because you HAVE a chance to buy King Tigers in perfectly "realistic" manner
That is, if you don't plan frequent upgrades. I upgraded just once a year.