The consensus seems to be, then, that you would have to reduce the enchantment bonuses for it to not become a total mess. So how do you think would be the best way to do that if you were just using items provided by WotC? Would you just stick to +1 to +3 items or would you reduce the enchantment bonuses of +1 to +6 items. Would you then say that each +2 = +1 (+1 would be +0, +5 would be +4 etc.) or would you just go by +1 per tier so +1 to +2 = +1, +3 to +4 = +2 and +5 to +6 = +3 ?
For your original stated aims, I'd go with some variation on both of those options. I'd word it a bit different, but it would amount to the same thing. Basically, I'd place a surcharge on +2 and +3 items such that they ended up costing what the +3 and +5 items did, respectively. Then cap it at +3. This gets a bit confusing though, because you might still want to allow some of the special abilities that don't start until +4 items, and you'll need to allow crit effects from inherent bonuses to stack as well. It's easy on paper, not so easy in the CB.
Ideally, the system would let you specify the range of inherent bonus you want for the campaign, and the item bonuses, and whether or not they stack, and how they affect crits. Then you could set them however you wanted. Lots of inherent, little magic? +1 to +6 inherent, +1 to +2 magic, stack. Have lots of powerful magic swords? Flip that, still stacked. And so on.
BTW, another way to do this for a different feel would be to simply let inherent and item bonuses stack, then cut out the differences elsewhere. You could, for example, cut out the math fix feats, and then charge a huge premium in point buy for stats over, say, 14. Or cut out the automatic stat bumps by level.
Of course, what they really out to do in the CB is make the +1/2 level formula something that we could tweak ourselves, holistically or by categories. If they did that, then you woudn't need math fixes or inherent bonuses or anything else to make it work. Just set the formula to +3/5 level or whatever and go. The people that wanted this all on paper can do the same thing in one page on the character advancement chart, the way BAB works in 3.*.