Most of what you're talking about is item-related. What about just plain old
spellcasting? A 12th level PHB Sorcerer (for instance) can be high-magic enough
without that many magic items or creation feats.
IME, both playing and listening to others, the real problems stem from a proliferation of items, and the ease of getting/making exactly the item you want.
Sorcerer's are naturally limited by the number of 'known' spells. Even at 12th level, they only have a selection of 6 spells above 3rd level. Granted they can be cast very often, but they are limited/specialized. If he is able to buy items to make him more well-rounded, he becomes much more powerful.
Now, in a low-magic campaign, like Grim-n-Gritty, that would still be too powerful; but I got the impression that the original poster just didn't want way high magic.
One of the problems I sometimes face is when players use their spells and items to
"bull" their way through certain situations. The way this tends to be handled in the
rulebooks is to increase the magical power of the opposition. Next thing you know,
you're back in a world with half-dragon archdukes and "town" wizards and every city
having clerics who can cast "true resurrection" etc. This is the kind of setting I'm
trying to avoid.
Also, I have found that parties where the mages are overpowering often are allowed to rest as needed, so they can go to an encounter, blow as many spells as they like, and then go back and rest; sort of like most computer games.
If there are repurcussions to leaving, they will be more likely to keep going, if they must keep going, they are more likely to hoard their spells till *really* needed, thus not as overpowering.
(Repurcussions: PC's are attacking a deserted temple to get an ancient relic. The attack, and leave to rest.
The Bad Guys now know they are being attacked, so they can better defend. They can set up an ambush, they can track the heroes to their camp. Heck, they could just take the relic and leave; try and hide somewhere else. Remember, one little attack in the middle of the night, and no memorizing for the next day...)
Remember, not bigger baddies, smarter baddies. It is a blast having a 10-12th level party get sent packing by a bunch of kobolds.
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