Frankly, I think this is one of the biggest problems. Finding a spell book meant a guaranteed surge in versatility, and a nigh-guaranteed surge in power. Literally no one else can match that; a Fighter getting a cool new sword can stab somewhat more effectively than before, or maybe fly or something. A Wizard finding a new spell book is transformed, especially if there are even a couple good spells in it. Doubly so in Ye Olden Dayse, when spells were often allowed to be brazenly OP.
So long as any one class can upend the game that way, where a single treasure can take one from feeble to forceful, weak to wonder-working, you have this problem. "Geek the mage," as Shadowrun puts it. Don't bother with the chromed-up street sam in your face (just run away) or her rigger-sniper friend sighting you from across the parking lot (just use cover), because they can be dealt with later. Kill the guy who can break the laws of physics first, almost always.
I don't see the connection between these ideas. If anything, it seems the reverse. When you only have 10 spells a day at absolute maximum, you cannot afford to spare one for a bubble bath. All of them need to be good spells worth their keep. With what you derisively call "cantrip spam," you can afford to "waste" spells on something esoteric or weird.