I had the same EVAP code. P1457. First off - sweet write up - I would have never found the bracket screw without your pictures. I had the CEL come on, checked the code at Auto Zoo - and they came back with P1457. I also went to Advanced Auto Parts; they would not give me the code they said it was a "Dealer only - no definition"
So I called Honda Parts - asking for the Shut Valve as you mentioned. They mentioned that is was "rarely" this item (though under my car it is rusted to hell under mine as well). Shocked they told me when they run the P1457 code at Honda it comes back as a failed by-pass solenoid. So I ordered that part - 80 bucks, it is the part directly to the left incased in a plastic cover on the pictures posted here. I removed that and replaced it (screw were rusted to hell too - had to drill them out of the steel bracket to get the solenoid out). Honda parts guy told me 90% of the time it is the bypass solenoid - and that is what they replace. Not to say it couldn't be the Shut Valve Solenoid... but they said the first thing they change is the By-Pass Solenoid. I mean who is going to take the time to run a smoke test ? SO that's what I did - re-set the CEL and haven't seen it again.... yet....
Thanks for the write up though it was really helpful.