I have just hit Ambassador for the year with 100 "nights" (probably another ~20 to come); USD27k spend and 70 real nights in a hotel. I don't live in the USA, in fact I'm in Asia so our average cost of a room is vastly below that of the USA. However a couple of treats, paying for the family in two rooms and so on all adds up. It's interesting that when you remove the free nights, I'm at an average of about USD450/night, but I feel I spend a lot less than this on the raw room rate.

Hence, if you're hitting the nights but not the spend target (as I did for many years on corporate travel btw) and Ambassador means a lot to you, I suggest you need to look more closely at personal stays where I see that I generally spend more as I need a bigger room, or look at other hotel expenditure, for example eating in the hotel restaurant when on business trips, which is probably poor value for money but will get your spend up.

Having a different spend target per region would be complicated to implement, and I imagine the Ambassador team's fixed costs are indeed covered at USD23k (remembering that it was an increase from USD20k last year, wonder if the staff saw a 15% raise), so you then get into the argument of why the US stayer should subsidise the non-US stayer. I remember BA used to have different requirements outside of the UK, but gave that up a long time ago.