Characters are balanced on the assumption that they have X amount of gold invested in items at any given level. Stat-boost item prices are calculated by figuring (bonus)^2 * 1,000. Thus, a +2 stat item costs 4,000 gp. A +4 stat item costs 16,000 gp. A +6 stat item costs 36,000 gp.
Additionally, you can make an item slotless, essentially allowing you to wear seven pairs of slotless gloves and gain the bonus from each of them, but slotless items cost twice as much as standard items.
Given this, you could wear one slotted +2 item plus two more slotless +2 items for 4000 + 8000 + 8000 = 20,000 gp, significantly less than a single +6 item. If you were to wear those items in different slots on your body, you'd save an extra 8,000 gp.
The game is balanced on the assumption that you will have spent either 16,000 or 24,000 more gold than you are proposing with your methods.
Let's try something. A wizard 20 has 880,000 gold to spend. If he could spend every bit of that on stackable, slotless +2 Intelligence items, he would have 880,000 - 4,000*15 (number of item slots on the body) = 820,000/8,000 = 102.5 + the 15 slotted items = 117 items of +2 Intelligence. This puts him at +234 Intelligence, or a +117 DC to all of his saving throws. If he crafted these items himself, he'd have twice as much. On top of this, he'd have ridiculous numbers of spells, which lets him prepare for very nearly any situation, and he would think up any possible contingency, since he'd have an IQ somewhere around 2,500.
Yeah, that's right. Two-thousand five-hundred. Now, consider the equivalent of that as Strength. With a two-handed weapon, someone with a Strength of 250 deals +125 damage with a light or one-handed weapon, +187 damage with a two-handed weapon. This character can kill a great wyrm gold dragon in one round -- guaranteed, since he will only miss on a 1. Additionally, for this person, a light load will be 4,644,337,115,725.82 tons. So never mind hitting that great wyrm red dragon with a sword; just pick it up and smash it into the nearest piece of planet that you can find.
Ridiculous much?
But I feel like I'm repeating an argument here.