Well it wouldnt hurt, plus it would offer a little leverage in that if you walk in with cash a) they know you are serious, and b) they will do what they can to keep you from walking out without a bike.
Remember, if you are going to the only Enfield dealer around and trying to buy his only GT, he probably won't move on price....but if its a bike he's had for a while or he has multiple bikes of the same model, then he should be more willing to negotiate. Above all, be confident and don't be afraid to ASK for a discount on the total out-the-door price