I have my old Hitachi DD from the late '70s. It's still on time. I buy the recommended value cartridge by AT. But, my records are kept very clean and that alone is a marked improvement over any treatment they got before. I used the peel-glue method on a lot of them and they had not sounded that good since they were new.
Simple test involves reading the credits on the album of who's doing/playing what and listening for their contributions. Still, the biggest improvement, yet again, in the vinyl arena, has been with speakers. The second has been the cleaning. Third, is nobody else touches them anymore. Finally is the fact that I don't wear the needle down to nothing, like I used to. Nothing is missing from the music, and I am not curious for any further improvement. Some of these albums I've had almost 50 years and they were used a lot over a period of about 15 years.
More than anything, I am surprised how well "I" actually took care of them, for them to even be in restorable condition by now. Also amazed how all the cheap cartridges did not hurt them. According to modern thoughts on this portion of the hobby, I should be seeing daylight thru the grooves by now.