I think it would be fine to make tank and healer stuff drop more often.

I'm not sure about caster stuff. Many groups would benefit from it dropping more, true. However, not everyone has one of each caster in their raids.
I think maybe a better choice would be to make physical dps share their armor among them. They could easily put dex on the monk/drg gear as well. Dex wouldn't benefit melee and str wouldn't help bard. So there is no harm in their gear having dex and str.
I don't think it's the best option though, but by the numbers it might be fair.