It really depends on the record. For example, The Beatles remasters that came out in 2009 were 100% necessary because the original CDs that came out in the 1980s were insanely awful, to the point where you couldn't hear basslines in certain songs. But the reissues sound completely beautiful, full, and lush and as cheesy as this will sound, the first time I heard them I felt like I was hearing these records for the first time. I remember reading all these reviews talking about how energetic and raw the pre-Rubber Soul albums were but never understanding it until I heard the reissues. The My Bloody Valentine remaster was similar.
Really it all depends on how and when the record was produced in the first place. An album recorded on analogue and released on vinyl, then merely transferred from vinyl to CD in the 80s is bound to sound like shit because the mastering isn't from the tapes. So a remaster for that stuff is oftentimes really necessary in order to not sound thin and tinny. But if you're talking an album like Nevermind that was already really slickly produced and always sounded big and beefy, then yeah, a remaster is pointless.
"I'll die before I surrender, Tim".