Have you noticed the thread with a similar - though not exact the same - question:

https://www.flyertalk.com/forum/inte...tus-worth.html

It might help you in finding an answer.

I assume, that you are not considering any lower hotels than CP and fully aware, that Ambassador does not get you anything in a CP? If you are into lounge access, why not use the points for stay and contact the hotel in advance by negotiating Lounge Access by e.g. paying the fee. Ambassador - at least in my experience - does not really get you a confirmed upgrade to club lounge or full breakfast.