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I'm not claiming that this is a perfect balancing fix, or anything, but it's part of me removing the "plus" items from the game.
Certainly, I was just pointing out something that had occurred to me about the fix as I was considering it.
P.S.: mucking with the numbers is part and parcel of D&D. Many class abilities, ranging from humble Iron Will to Divine Grace, are designed to do just that. You're investing resources into saying "I'm really really good at this so it's unlikely that I'll fail." I think the idea of "maintenance" magic items is dumb, it's just a trap for newbies, but the idea of someone committing resources to being the hardiest in the land or having a tower of iron will not only seems fine to me, but good.
It is part and parcel to 3E, and it's a lot of what I don't like about the game. If that's something you like, then you might not like my set of rules that I'm using. My line of thinking was this:
When you're telling stories about the game, no one cares about your Amulet of Natural Armor, and no one cares about how big of a plus you got on it. Sure, it's part of the game, and it can be fun figuring out how to get the most plusses for your gold, but it doesn't make for interesting stories, and it makes for really boring items. Any random PC I roll needs to have roughly half a dozen stock items just to function, and I find it so trite and bland. I wanted items to be something that people would care about more because they were interesting and because they did things, rather than just keeping them on the RNG. So, I dropped all the RNG-modding items, and handed out the bonuses for free. Now, you don't have to worry about dropping your AC by a point to get that Hat of Disguise.
I am very sympathetic to this. There is a slight counterpoint with regards to things like Girdles of Giant Strength (viz. Thor), but with that extremely nitpicky point aside I wholeheartedly agreed.
My, admittedly kludgy, approach has been to essentially bury magic items "under the hood." In a lot of campaigns we distinguish between items that exist within the narrative, an actual hat of disguise that can be traded, etc., and things that are just game concepts like feats and classes are. In many of our campaigns -- about 60% of the ones we've played in the past year -- we've even divorced "treasure" in the sense of magic items and things that do stuff from wealth. This way the average PC isn't rich as Croesus after a few levels, and you can distinguish rich characters (either PCs or NPCs) for fluff purposes from others.
Like I said, it's a bit kludgy as there's a bit of an incentive to hide some items away from the narrative, though we rarely sunder or steal magic items anyway, and doesn't get rid of the "maintenance" items which RobbyPants' system elegantly does. If it were to come up, I might aim for a hybrid system, where maintenance was taken care of so that everyone had the "appropriate" bonuses and could then devote resources as they see fit. I'm not against exceptionally good swords, even for magic ones, but I do hate maintenance items.
This is way off topic as well, but I do sort of like random magic items. They can be neat and add something unexpected to the character, and there's a nice linkage there with fantasy literature (e.g., Perseus' invisibility helm). Too often they get swept by the wayside, though, b/c (i) they are a ton of niggling things to keep track of and I have developed a keen hatred for bookkeeping, (ii) they aren't things you need or are eclipsed by other priorities. I've had games where informally there were some items or some proportion of items and WBL that were up for optimization, selling, crafting, etc. And some, often those that were way overpriced for their utility, that were "off limits" and there for us to use but not sell, etc.