If you read the MH thread you will see information about upgrades over there. They do not upgrade Diamonds to a suite, but to maximize the value of Diamond you can book the basic room, then they upgrade you to an exec room, and from there you pay 1000 THB extra for the final step to bring you up to the panoramic suite. You can do all this guaranteed at time of booking if you contact the hotel directly to arrange it and it will be cheaper than booking the panoramic suite straight up because as you pointed out in that case you do not get any upgrade.

In any event, in light of your second batch of comments, like others I would recommend WA. If you have appreciated WA Amsterdam and have good memories of it, you are more likely to have this kind of experience at WA Bangkok than MH. While I respect @alanslegal 's opinion and not to take anything away from Pen, personally I prefer the new & shiny hardware of WA than the aging Pen at this point in time. Maybe in a few years the equation would be different.

Also you mentioned that you value a great breakfast, so WA will be a good fit. Breakfast at WA beats PH and StR easily and even more so compared to MH. You should have no problem with 1pm check-out as Diamond. I also confirm [MENTION=777305]thbe[/MENTION] 's observation that WA can come down to 6.75k THB during sales. One time I was able to find a Best Rate Guarantee and paid 5.4k THB; it is not the easiest property to score a BRG so I would not count on it but it's doable.