I feel there should be a permenent one, although it should cost more than 500 rcs.
I think its safe to say most people only use the CoR in two circumstances.
1) Luck cloak runs.
2) Clan wars.
I believe it was Tananda that first stated they should not be allowed in clan wars, which I fully agree with. And if you remove clan wars from the equation, is there any reason why they shouldn't be permanent?