I assume you plan on running a mixer system?
I think it is a worthwhile option if you can be bothered setting it up, and really should't be written off as quickly as everyone suggests.
Yes if you use a mixer system you will lose a bit of power over a petrol setup, but if it's not an all out race motor where every kw counts who cares?
For a street car wouldn't you rather get heaps of driving at a cheap price, rather than pay a large fuel bill for a little more power? If you setup the cam/ignition to suit there is no reason why
it can't be a pretty decent motor that will cost you bugger all to run. Another consideration is the rebate available. It can be far more expensive to get a decent set of sideys setup, than put on a dedicated gas system with a rebate.
If you were getting really serious then you could consider a liquid injection setup, which would actually pickup power over petrol! But this would not be cheap.
Also if you are worried about the power figures, you could always run a turbo setup...
IMO it is definitely worth the thought, do something different! :)