I like your approach to speed up combat, although I inevitably will have to look up stuff and I would understand if my players would view it as unfair if only they have to skip their turn while this wouldn't apply to NPCs.
We have repeatedly debated the matter of spells for almost a year while never quite reaching a consensus. I understand your opinion on winning D&D, I just think that the game will not be able to develop any depth anymore if the preparation can't be relied on, being replaced by an inflation of poorly thought through plot hooks made up on the spot.
Did one of your spellcasters know the Gate spell? If so, what stopped the PCs from pulling the BBEG out of their lair and beating them up from the comfort of their homes? I'm having trouble coming up with challenges that don't actively oppose the abilities of high-level PCs. Just saying 'no' and refusing to let a spell take normal effect would very likely seem unfair, no matter how logical the in-game explanation might seem.