Am I doing a horrible mistake in improving dragonhide drastically?

[Dr TPK]

I allowed my players to vote on how dragonhide should be treated in my game. I had several options and one seemed most popular:
Dragonhide armors grant Energy Resistance 5. The energy is the same as the dragon's immunity (if any). The price of dragonhide armors are increased by 5000 gp.

Have I committed a terrible mistake? I know that this might've been better in the Homebrew section, but I still thought it might be best here, since it's a house rule.

[Troacctid]

Oh, you don't need a houserule for that--it's just dragoncraft armor, from Draconomicon, page 117.

[Dr TPK]

Oh, you don't need a houserule for that--it's just dragoncraft armor, from Draconomicon, page 117.

Now that is very interesting indeed... Thank, Troacctid!