I can't speak to all of your options, but let me comment on some of what may be "unknown" to you.

1. The Four Points and Sheraton on the river are great values and great and opposite locations - close to all the activity (food, shopping, nightlife) or relaxing on the river,close to the Grand Palace.
2. Western breakfast (eggs and toast and coffee) is easy and cheap to get in Bangkok if you don't need to get a huge spread that will keep you full. Also, Bangkok has great food, so you are better off with a light breakfast so you can eat thai food the rest of the day. The availability is definitely true for the Four Points - I am not sure what cheap options are avaialble by the river. There is a McDonald's around the corner of the Four points if that is your idea of a western breakfast, but there are cafe type places as well.
3. The Aloft is a category 1 so it can be even cheaper if you are counting your points or money.
4. Cash and Points or weekend discounted points (3,000 points for category 2) are such good options that I would maximize these stays and spend the saved cash at a luxury property for the days I can afford.
5. Upgrades are easy and nice in BKK, but the base rooms are fine with great airconditioning-if there is just 2 of you, you don't need more in Bangkok!

My bottom line is I would not worry about getting a nicer hotel than the Sheraton or Four Points unless you wanted an "aspirational" stay such as the Mandarin Oriental or Sukhothai. Maybe even a 1 night stay there. The Conrad or Hilton are only incrementally better than the SPG properties and I would rather save and splurge in Bangkok where saving means staying at a really, really good property such as the Four Points.