Lots of good feedback.
As a credit card touring 'expert'
myself, I'd say go light as possible,
With that in mind, before you buy, consider this- do you have any other rides you think you might do in the future? For example, longer rides? etc... If that's the case, perhaps a rear rack and rear bags would be the bomb. For the ride you mentioned, a rack and one rear bag would be enough, but the platform gives huge flexibility, and would integrate into future possibilities.
One thing I like about a rack, it that with a mesh tie down, you can pretty much tie whatever you want to it. Tonight, it was warm, and my jacket was sweaty, so I tied my jacket to it. I could have just as easily tied a bottle of water, wine, or a some food from a store (to take back to hotel) , etc.
That's not knocking the rear seatpost bag setup. of handlebar bag.... I like that too. Lighter, keep it simple..etc...
Another idea- lay out all the stuff you think you need on a table. Second pair of shorts/jersey/light rain jacket, real shirt/shorts/socks/(apre ride/dinner) toothbrush... How much space does it take up? Let this guide the decision. For your ride, you don't need much.
edit- One thing I like in the pics above is the top tube bag. That's a great place to store food/ goo's etc.. to keep it separated from your main gear. You don't want your spent gels/power bar wrappers mixed with your main gear.