I certainly feel that a Cobra on restricted rego would be worth less. Certainly less appealing to purchase. That's assuming it cannot be full registered.
Are the rules different down in Vic, but in QLD you don't have free reign to drive the vehicle anywhere you want. Your restricted to club events, repairs, charity events, ceremonies for family members etc etc. I know this gives a bit of scope, but doesn't give you free reign.
One of the things that attracted me originally to Cobra's, was the ability of full registration.
But hey, I'm all for people using restricted rego, if that's the way they want to go.