Increased weapon damage as if weapon was bigger

[Cicciograna]

For my upcoming campaign, I'd like to try out a new rule. Since I'd like to make weapons more relevant and deadlier, I was thinking to increase the damage dealt by each weapon as if it was two sizes bigger.
I recognize that this would have a great impact on game at very low levels, but how would it work, say, from level 6 onward?

[jaybird]

Light and One-Handed weapons don't get much of a boost, usually going up an average of 2 damage (1d4 dagger -> 1d6 -> 1d8). Two-Handed weapons get a substantial boost to the tune of 7 damage or so (2d6 greatsword -> 3d6 -> 4d6).

[Spiryt]

I would probably somehow make it based on certain BaB/whatever level - this way warrior types could deal more damage, and make weapon damage matter at least a bit even on later levels.

While it wouldn't imbalance low levels and 'normal' npc so much.

One would have to look out for some weapon size increasing tricks then, could quickly get funky with those.

[Fenryr]

Be warned with Strongarm bracers, Platinum/Gold weapons and Powerful Build or Monkey Grip and Bashing Shields. They increase size at least once. Nothing too big but it may surprise you.

[herrhauptmann]

Be warned with Strongarm bracers, Platinum/Gold weapons and Powerful Build or Monkey Grip and Bashing Shields. They increase size at least once. Nothing too big but it may surprise you.

Mind you, platinum/gold weapons (Magic of Faerun, not PF versions) will require some common sense. They were written for 3.0, which doesn't work quite right in 3.5/PF.

[NeedsAnswersNao]

Ask PlzBreakMyCampaign (He's still over at BG). He has the most comprehensive collection of what you are asking for.