Once you get to higher levels, the first combat or two means PCs going absolutely nuclear. I think you need 3 to 5 combats to challenge lv 5 and above. They can handle the heat. If you do less, go way over CR
If I specify "Very Rare Magic Item" it gives a parameter, and even arbitrary parameters can help. It also gets the players thinking I'm concerned in some way with game balance, and though it's true that I'm not, it gives the appearance of that. Someone else was going on about "why don't they...
It's not just destroying the items, its also destroying the formulas that make the items possible. The concept behind the item is wholly destroyed leaving no ability of making anything similar again.
The last part has been stated by previous posters already, but having a campaign arc and planned twists is not "the worst excesses of '80s-90's GM-plotted trad RPGs". One of the top selling D&D adventurers is the Curse of Strahd. Are there planned twists there? Is Balder's Gate: Ascent into...