I don't subscribe, but I've given them my email a handful of times to receive free samples of books. (They're extremely generous with this. In a couple of cases, they sent easily half a book as a free sample.)
My experience has been that they're on the low-volume end of the "we have your email" spectrum. Not nothing, but not hideous.
I've subscribed to their forums with an email that I link to them, so I know for a fact that they spam. They also write articles that are really paid for ads, so the shady meter for sitepoint.com is over toward the orange side of the scale... but, you know... you gotta make money I guess.
Do you have 'Receive Email from Administrators' enabled on your account? I do, which is I assume why they occasionally email offers and is also why I don't consider them spammers. I do agree with you that their content has slipped in recent years though.
My experience has been that they're on the low-volume end of the "we have your email" spectrum. Not nothing, but not hideous.