I first signed up for Ambassador in late 2001 because I had a stay at a property in Rio -- the initial free weekend night paid for the cost of the membership. Never expected I would still have it active nearly 20 years later, but each year I have found an opportunity to use my membership worth keeping the membership. Often that is the free weekend night - even now with a slightly higher rate on the paid night since you have to book an Ambassador rate (a change a few years ago). But actually the past two years I have not even used my free night -- but it has still been worth it for the room upgrades as work has me staying at the IC Strings in Tokyo several times per year.
As
NativePhD pointed out definitely reach out to the hotel when you are considering making a reservation. Most have a clear upgrade path defined from the room you book to where they will put an Ambassador, so usually they can tell you exactly the room upgrade you will get -- and then you can judge the value based on the rate you will pay. As an example earlier this year I was looking for 9 nights in Hong Kong for this holiday season (before the protests started) and was trying to find my best price for a suite (with separated bedroom) with a harbor view and including breakfast (and a hotel that would let us have 2 small children in the room with us). The IC Grand Stanford ended up being the best deal I could find in the city because of the upgrade they confirmed at time of booking - even though I was paying for a Club Intercontinental room to get breakfast vs. getting that for free at Hilton or Marriott. Ended up changing things because of the protests but I would have assigned at least $100/night value to that compared to the other options that would have worked for me at the time I was reserving.
Also always check the prevailing rates vs. what you can buy the points for and then redeem at ICs. There are threads on here discussing - but often the max points for an IC hotel night can be a good deal in large cities like NYC or Tokyo, especially when you then consider the Ambassador benefits for the stay.