Ethereum is a platform that still has 2 years of major development followed by a lifetime of continued minor development.
So every time the devs manage to push an upgrade to a testnet, every time there are no major bugs, every time the main net is upgraded. All of this shows progress in ethereum, it shows that the devs are delivering on their roadmap and their schedule.
It is this progress that will increase the price. Announced upgrades and plans can not show that devs are delivering and will therefore not increase investors confidence that we will get to the promised finish line 2 years from now. Only delivered products will do that.
That is not to say that the announced upgrades do nothing, they show where the devs hope ethereum is going. And how investors see this vision does move the market. It is this movement that I feel is long priced in.
Byzantium is the first stage of the Metropolis upgrade and will be released in the next 36 hours and if no major bugs show up in the first few days this should increase investor's confidence.
And again in the next few weeks when/if it is pushed on the mainnet without problems we should see another increase in confidence on the future of ethereum. The potential rise and fall should be much bigger for this release as it is not uncommon for bugs to be found on the testnet release.
I expect this to be a binary reaction. If Byzantium ships with no problems the basic value of ethereum will be increased and the price will likely reflect that. And if there are bugs the trust in the devs achieving their goals will be damaged and the value of ethereum will fall, again probably with the price.
I give the distinction between the price and value because the market is a chaotic beast and other factors (like the china ban) could easily move price independent of the expectation of devs achieving goals. Look to the btc/eth ratio for a better reflection in this.
Disclaimer
Please do not invest on the advice of a stranger on the internet, only use this advice here as a starting point for your own research, and then if you choose to invest please only invest an amount that you can afford to lose.