It should be patently obvious that the GUI will have an effect on price, not just for faciliating greater user adoption but also for being a point of speculative propaganda.
Monero's all-time high is 0.01 which was achieved based on the expectation of Mintpal adoption - a meaningless exchange that has since departed.
The rise of ETH and fall of Cryptsy/Dash has pushed new wealth and whales into Poloniex from which XMR is the primary beneficiary.
Monero is a uniquely attractive tripod that posesses an extrordinary technological component, a credible political base, as well as demonstrable speculative volume.
This means that at any point in time the XMR price can explode without warning and for no reason whatsoever, other than the fact the price is deemed to be very low, and the long-term confidence is deemed to be very high.
Yes, Monero is wobbling on the tipping point and could at any moment fall upwards into a much higher price range.
A GUI will help catalyze the sustained cosmic background levels of adoption/buying pressure needed to offset emission and overwhelm profit-taking supply pressure on the way up.
I like the "uniquely attractive tripod" observation about XMR's critical masses of tech+people+money, as it is congruent with the decentralized+private+digital Monero trivium that I've made my avatar.
