Twowolves said:
That that kind of "risk" was very easily taken advantage of, and could be seen as picking on the character when the gamble didn't pay off. It's one thing to have an ability negated by a monster as a plot point or adventure challenge (like a Beholder's Anti-Magic cone, or the "you wake up naked" adventure hook), but it's another to have an unusual vulnerability like that. Now either the DM avoids Dispel Magic or Anti-Magic situations or else it has a compounded affect on the risk taking character, which could be perceived as intentionally punishing a character for obtaining a feat/PrC this way.
You don't need magical stat boosting items to be vulnerable to not meeting prerequisites for feats. Heck, it doesn't even take a 3rd level spell.
Ray of enfeeblement is a 1st level spell, and it can make almost any fighter unable to qualify for Power Attack, or any other feat with a strength requirement.
From the new Spell Compendium, the Ray of Clumsiness does the same thing for Dexterity and any feat with Dex as a prerequisite.
The 2nd level spell Touch of Idiocy reduces all three mental stats at once. You can lose access to Combat Expertise, Improved Trip, Improved Disarm, Natural spell, etc.
That's not even mentioning the poisons and diseases that can damage various stats.
Heck, I have a character who eventually bought Gloves of Dexterity +2 because he was tired of losing access to Dodge and Mobility everytime he used the Enlarge Person spell. That's not going to stop him from losing access to them if he get's hit with a Ray of Clumsiness though.
And all of these spells last much longer than the 1d4 rounds that a succesful targeted Dispel Magic lasts. None of them allow saving throws either, while Dispel Magic requires a succesful level check. They do require touch attacks, but those are much easier to succeed at.
Choosing to use a magic item to qualify for a feat leaves you no more vulnerable than qualifying with an unadjusted stat.
Using a magic item to help you qualify for a PRC is pretty hard to do (outside of meeting stat requirements), and is usually an obviously poorer choice than just meeting the requirements normally.