Argyle King
Legend
In 3E and earlier editions, a caster was not nearly as good at using magic items as a fighter. Give both more gear, and a fighter gains power relative to the wizard. So, if you want to have a gear.neutral power scaling, you have to change things so that wizards benefit as much from their gear as fighters do. Until you do that, expected wealth level has to be a part of the power equation.
And it turns out that is quite tricky to do, because the same bonus applied to different classes works out very differently. A bonus of +1 damage per attack is a lot better if you have several attacks (like the fighter), and an increase in AC is more valuable if you start out at a better AC and get attacked more (again like a fighter).
This is one of the things 4E did better than previous editions, introducing implements.
Going back tot he basic discussion, I'd say spells should still auto scale, because even without magic items, fighters also auto scale. And without some kind of scaling damage (and assuming scaling hp), fights will get very slow.
I strongly disagree with the part I bolded. Both sorcerer and bard have charisma as a primary stat; charisma is what is used for Use Magic Device, and (if I recall correctly) Use Magic Device is a class skill for both of them. It's been quite a while since I have played 3rd, but I believe that means that both of those classes can trick magic items into working for them; even items which they would not normally be able to use.
Also, keep in mind that a caster doesn't need a weapon or armor. The magic they have comes from them. This means they can instead take the money which would be spent on those items to buy other things for the part such as a wand of a healing spell; nystul's marvelous pigments (which are extremely useful), and others.
A third point to bring up is what happens when items are removed. There are numerous scenarios in which you may not have access to items. In such a scenario, the fighter becomes a commoner with a better BAB and a bunch of feats. The caster still has all of his power.
I think reducing item dependency is something D&D needs to put more effort into.