Data point:

Booked corner room at Conrad Bangkok for 2 nights using cheap US Swimming rate. Nor1 price for exec suite 3100 THB.
Pre-upgraded night before to exec corner room. Checked nor1 on website immediately and found price reduced to 1996, so ticked box.

At check in yesterday, granted nor1, and given a further complimentary upgrade to a massive Deluxe Suite!

I have thus paid 6900 THB++ per night for a Deluxe Suite compared to over 11000 THB++ at time of booking.

I maintain that, for the average diamond, a great strategy can be summed up as:

Book the room you would be comfortable with using whatever MVP / Public sector / cheap rates you can find, then monitor nor1 / negotiate at check in to secure a suite. You may find you see the inside of some quite amazing suites for considerable discounts. It's not as dramatic as getting a free upgrade, but it happens a lot more often.

Postscript:

I only wish I had more friends in BKK to host an appropriately opulent soirée here!