I've been using the XPH pretty much since it came out, as my group tends to like the psionics flavor, so over the years we've put it through its paces.
In my experience, psions are somewhere near the top of the power curve. Better than sorcerers, but not nearly as versatile as wizards. And if they're trying to end a fight quickly, psions burn through their PP allotment FAST! So definitely, if you want to keep the psion's player challenged and interested, you have to make it a regular possibility that they will run dry, and force them into "PP-conservation mode" early.
That said, I would argue that the warmage is probably roughly equivalent to a kineticist. The kineticist can squeeze out a little more damage per round, but the warmage just keeps going and going and going... Certainly, I've found that the warmage outclasses non-kineticist psions in terms of raw damage output, so depending on what your players want to play, this may or may not be an issue.
To keep things sane, my house rules do include minor tweaks to energy missile (some of the energy conducts to other grappling targets, Save DC increases +1 per 2 PP spent), and if you allow Expanded Knowledge to be taken only once, it really cuts down on the cherry-picking of powers from other disciplines' power lists (do I take the feat at 5th and pick up energy missile or wait until 9th to grab psionic dominate?).
But yes, if you wish to include psionics in your game, you will likely need to tweak the rules a bit to suit your style of play. That said, however, this can be said for pretty much any other supplement that gets released. In my experience, for my group's play-style at least, psionics is most definitely worth it.
Cheers,
Vurt