Well, I've been to all of these (including recently) and plenty of other places. I would personally drop CGK, in fact, I would probably leave anything in Indonesia for a future trip. Most of your mileage will be on the long-haul routes anyway. I think you have 2 conceptual options:

1) The City tour--SIN (2 days), KUL (2 days), BKK (balance) or vice versa, and do as open-jaws routing if you can. Singapore and Kuala Lumpur really don't require more than 2 days each. Bangkok has more things of interest to most tourists in terms of sheer volume.

2) The Country strategy--in which case (a) would be to BKK with 3 days there and the rest in either Thailand north (culture) or south (beach) areas. Or (b) SIN + KUL augmented by things like Melaka or Penang or Cameron Highlands in Malaysia.

If your mileage earning needs are such that you really need to go the extra distance to Indonesia, then I agree with the above poster and would go to Bali for the entire time, and I would route there directly via SIN or KUL rather than through CGK.

I would not advocate going to Vietnam on such a short trip when there are so many other options that don't require visas. And I disagree with the above poster about Saigon: it ain't that great unless you're a single guy looking for... To go to Vietnam for 3 days in Saigon is pretty much not cost-effective--see it as part of a longer Vietnam trip in the future.