CRGreathouse said:
A +3 longsword costs 18,315 gp.
Two +2 shortswords cost 16,620 gp.
It's not too bad.
Yes, but it is also not the right comparison - you are wasting a hand. You are comparing a longsword (a one handed weapon) with two shortswords - two light weapons.
If you're looking to maximize damage, compare a two handed weapon (say, a greatsword) with two light weapons (two shortswords).
Even if we turn that longsword into a greatsword, we don't actually expect much (if any) benefit to the two shortswords in damage - the two shortsowrds have one extra point of enhancement bonus, but they will each hit less often. The enhancement bonus to damage isn't the real issue.
You start seeing notably greater damage potential when you start adding extra dice of damage - from, say a flaming weapon. Two flaming +2 shorswords cost in the neighborhood of 36,000 gp. One +2 holy weapon costs around 32,000. Still, not too bad, you might say. But the extra 4,000 gp is equivalent to a whole list of lesser items - including gaultlets of ogre power, or a set of boots and cloak of elvenkind...
And that's if the DM in question allows you to get whatever weapons you want, whenever you want them, at DMG prices. While many may allow that, many don't. If the player is going to min/max, he should take into account how likely he is to get the items required to take greatest advantage of his feat choices.