I would say 4 Pips, but I realize that not everybody is Max level with 100% Power Pip chance. So I'll have to go with 3 Pips, though it isn't preferred.
Why raise the Pip cost, you ask? Well, have you ever faced a Wizard of your own school from second in PVP? Of course you have. Ever wondered whether or not you should hit with a potentially game-changing spell, but decided against it because you are going second, and might be dispelled? I know I have. (And if you haven't yet, you will start to once you rank up higher).
I personally find facing my own school from second at the higher ranks...irritating to say the least, because I know I will be dispel spammed (and I almost always am).
There are players that carry literally ten to twenty dispels, some of them not even of their own school. Depending on my playstyle, I usually pack 6-8, myself, if only to get rid of my opponents' dispels...
Yes, Dispelling can and should be a strategic factor in PVP, but not every turn. Something has to be done here, I feel.
PVP going from second should NOT be a guessing game as to whether or not you're going to be dispelled. Going second can be hard enough without this extra problem.
On a side note, Jades love dispels, especially Unbalance. Fires love dispels, Lifes love dispels. Everybody loves dispels. It's tiring, and I feel there should be a greater penalty for trying to dispel an opponent. All anybody has to do is slap on an Elucidate TC onto a Dispel, and voila, a 0 pip Dispel is born. (And yes this happens. Often. I've done it myself, but I don't condone it.).
So, in conclusion, single dispels, like Dissipate, Quench, or Unbalance, should cost 3 Pips. (or 4). And to be frank, anybody who could actually disagree with this suggestion either doesn't know how much of a factor this is at top level (e.g. a low-level player) or needs some more coffee.
If you made dispels cost more pips then some boss battles would become even harder for a lot of classes that have to cast other school dispels. Case in point - the rat in Polaris. The only way to manage his minion summoning properly is to throw up fire dispels like crazy on him. If you don't have a fire, two pips is kind of manageable for an off-school spell - but 3 or 4 pips? No way.
Same with some of the Darkmoor bosses. Storm and Death dispels are really needed in a lot of battles. I think the 2 pips is just fine. I rarely carry dispels for normal battles. I only carry them for the really tough bosses. I cannot speak for PVP players though, since I only do PVE.
If you made dispels cost more pips then some boss battles would become even harder for a lot of classes that have to cast other school dispels. Case in point - the rat in Polaris. The only way to manage his minion summoning properly is to throw up fire dispels like crazy on him. If you don't have a fire, two pips is kind of manageable for an off-school spell - but 3 or 4 pips? No way.
Same with some of the Darkmoor bosses. Storm and Death dispels are really needed in a lot of battles. I think the 2 pips is just fine. I rarely carry dispels for normal battles. I only carry them for the really tough bosses. I cannot speak for PVP players though, since I only do PVE.
Actually a more efficient way to deal with the Rat is to have a , , , or with pierce 21% or higher enchant their X or 4 Pip AOE cards with Unstoppable to take care of the minions on their second regeneration. No dispels needed ever. Or everybody can heal on the first round and every 3 rounds thereafter to activate the healing minion cheat...but that's besides the point.
Dispelling isn't really a strategy when it can be spammed every turn, and seeing as you only do PVE...well. You should watch a Max level Warlord Balance vs Balance match at the Arena to see what happens (they spam dispels like crazy, me included). And besides, it is not meant to be 'manageable'. In terms of PVP, 2 Pips is far too little when you can stop an entire combo with one little dispel. 3 is much better, and in terms of PVE...well, use Empower, Elucidate / Simplify, or a Mastery Amulet. Of course it will make things 'harder', or more strategic, but I thought that was the point of crazy dungeons like Darkmoor.
I think that dispels should stay at 2 because they don't always come in handy. it only depends on the type of element your opponent has. I don't really think it is an issue, but whatever!
dispels, Lifes love 
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, or 
with pierce 21% or higher enchant their X or 4 Pip AOE cards with Unstoppable to take care of the minions on their second regeneration. No dispels needed ever. Or everybody can heal on the first round and every 3 rounds thereafter to activate the healing minion cheat...but that's besides the point.