I was planning a short-term holiday for a minimal spend, and some searching in Marriott's reward space brought me to Turkey, Spain and Italy. Especially in Spain, there are many AC hotels in the lowest two reward categories (1 and 2), costing 7,5 / 12,5 K points per night. For a five night stay (fifth night is free for Marriot rewards) that amounts to 30K / 50 K points.
I also wanted a hotel relatively near the railway station (AC hotels are often a few kilometres outside the city center). Given a minimum spend and nearness of a railway station, as well as a decent review score, I ended up at the AC Hotel Brescia. Brescia is an awful city if you approach it by rail - many European cities are, for obvious reasons. But the town itself is rather nice, and it is centrally located somewhere between Milan and Venice in northern Italy.
Cash rates for this hotel are currently a whopping 150 euros per night, which would value the stay at 750 euro and the value per Marriott point at 2,5 cents. I would put my 150 euro probably in a more centrally located hotel, but the value here is still amazing (well, we still have to complete the stay so how amazing it really is will be in this blog later on). Remember you get 20,000 AMEX points with a platinum card and AMEX values those at 80 cash value.
For 30K AMEX points this would mean you multiply its value from 120 euros (conversion from AMEX to Marriott points is at a 1:1 rate in the Netherlands) to 750 euros, i.e. from 0,4 cent to 2,5 cent, multiplying its value by six times. Remember though, readers, this is all theoretical, the 'money' is not much more real than a bitcoin.
UPDATE: our stay appeared to be during the Mille Miglia event - which would in part explain the relatively high cash prices of the hotel. The hotel is perfectly fine, but it is not in the best neighbourhood you could imagine. Basically, it is in the middle of largely abandoned buildings. We walked back late in the evening every day and nothing strange happened, but I wouldn't recommend walking around alone in the area.