a formula is not a bad thing when upgrading and you are a beginner.
Luckily I never had the budget to have to limit my upgrade by a formula, I always went all out and spent 100s of dollars!
"You spent how much on that cartridge?"
Should there be a ratio of the amount of vinyl to the cost of your playback system? A recent thread implied that you should not have a nice rig unless you own a lot of albums. Almost like one does not qualify.
I want to enjoy listening to the relative-to-some few that I own without compromising. I agree that if you have little to no familiarity with the format, you should enter gingerly. But once you've decided you like it, why accept mediocrity?