If you're flying into BKK, you'll see a tourist desk at the luggage pick-up area. These are licensed guides. We booked a tour through them at less than half what our hotel was charging. BKK is a very safe city, so it's easy to wander without a guide, but having a guide/deriver will make sure you get to some of the "must see's" on your list.
I agree with the basic list, though I disagree that the Jim Thompson house isn't a biggee. For me, it was one of the highlights, but then, I love architecture and I love the story of his life.
I would also add to the list a visit to the PatPong area at night. There are two arrtactions here - the night market that sells everything under the sun....(okay the moon!) and the strip clubs. If you'd like to visit any, stick to the ones owned by the King organization (it's posted on the outside), these are legitimate and you won't have any problems w/ drink scams, etc. I went with my husband and was warmly welcomed at the clubs.

I've been to BKK twice and stayed at the Shangri-La once and thought it was just so-so, not nearly as lovely as the Shangri-La in HK. On the other trip we stayed in the Erawan Grand Hyatt which was an excellent hotel. It's a city location, as opposed to being on the water, and we were able to walk to alot of places.
If you prefer staying on the water, I'd choose the Mandarin or the Peninsula.

CJ