As these other guys have pointed out, the DMG tables are guidelines for the DM to ballpark the price of a new item he wants to make, NOT construction rules for the players. So first, you'd have to allow the item to exist in the first place (bad idea), then you'd have to set the price (aim high)...
In smackdown-type threads, I've seen people suggest ridiculous characters using this. One person said "Oh, I'll have a STR of 48, because I made an item that gave a +6 Enhancement bonus to STR, another that gave a +6 Luck bonus to STR, another that gave a +6 Sacred bonus to STR..."
Allowing the player to research a new type of item isn't always a bad idea, but it shouldn't just be the same old item in a new slot (for example, someone suggesting an amulet that does the same thing as their favorite ring so that they don't need to take the Forge Ring feat). And, as DM, feel free to add some drawbacks or added abilities. For example, if someone wants an item that adds Natural Armor and CON, make it also add a bit of DR and subtract some WIS, then price accordingly.
There are just some insanely abuseable combos that you should ban outright (the infinite Cure Minor Wounds or True Strike come to mind), but in my experience they've all been traced back to three things:
1> Spells with instantaneous or really short durations (not as much of a problem in 3.5E)
2> Spells that have a good effect at caster level 1
3> Spells that are useful when cast more than four times a day, especially if they can be cast on other people.
It's when those three are combined that the rules really break. If your item of Cure Light Wounds was a caster level 12 ring, it wouldn't be quite so broken. If it was a spell like Longstrider that has a decent duration and is self-only, it's not an issue either.
That led to the House Rules that my group use:
1> Any item with unlimited uses or continuous effect must be a Rod or Ring. (Existing Wondrous items with unlimited/continuous use are retroactively changed to 5/day)
This was based on Monte Cook's "quacks like a duck" statement.
2> All items have a minimum caster level equal to the level needed for their Feat. So, no ring can be below CL 12, no Wondrous item below CL 3. Also, all abilities on an item must have the same caster level.
This solved 99% of our problems before 3.5E redid the system. Boots of Springing and Striding weren't a problem any more, since they'd only last a couple minutes at a time and required activation. It's a LOT harder to break the system when you can't have unlimited uses.