For me, it is about $20 a night for the club access and about $60 for the 4 pm checkout. (I don't always want or need 4 pm checkout) This is highly subjective, of course.
So if I plan to stay at SPG hotels 20 nights and want two 4 pm checkouts for a particular year, it will be worth $520 for that year.
I did not count the extra points I would get as a gold.