not necessarily that RC4 will have an impact on the price short term, in fact a slight drop wont be surprising, I know that most people wont agree (I hope I am wrong)....before you tell me "but the price skyrocketed when RC3 was released" yes true, the price skyrocketed but not because of RC3 but because of a whale investing a shit load of BTC in DRK....
The price doesn't matter in the short term. What matters that is there are no critical bugs in RC4 and that users can finally send coins anonymously. Adoption and actual use of the coin begins at this point.
As long as update goes smooth , price change will happen accordingly and no need to worry about that.