I have never come across a re-pad intended to assist with erosion. That sounds like a recipe for disaster to me. The prime purpose of an elbow re-pad is to assist with local stresses where a trunnion or similar is attached.

As regards flexibility, the combination of pad and attachment such as a trunnion at an elbow will effectively destroy any flexibility and strictly speaking, its s.i.f's. However the prudent way to model this would be to ignore the bend element and its flex factor, but manually add the normal s.i.f's to the bend node.

I agree with Ed Klein, a re-pad is far more practical than a thicker bend.