Yes.
+1 to damage is pretty standard for a feat in heroic tier. It doesn't scale, but it's untyped, so it stacks with everything.Two Weapon Fighting seems like a pretty crappy feat. However, it is a prerequisite for somewhat less crappy feats such as Two Weapon Defense and Two Weapon Flurry.
Perhaps in future volumes it will be replaced with an Improve Two Weapon Fighting feat, although more likely it would be a prerequisite for such a feat.
If you're talking about Twin Strike, no; the feat says "you gain a +1 bonus to damage rolls with your main weapon." Blade Cascade sort of does; each main-hand attack gets the bonus and each off-hand attack doesn't, so you alternate "yes" and "no". Other attacks like Passing Attack, Fangs of Steel, or Weaponsoul Dance do get the bonus on every attack.If you have a power that lets you attack twice do you add the extra damage from TWF twice as well?