I'd say that SEO spam is not always deleted fast and I don't think it should be discouraged to report this if it is older than 6 months.
I still report old spam, and it still gets deleted. The Old post warning isn't meant to keep spam:
Old post: We generally do not moderate posts this old for on-topicness, substantiveness, multi-posting, and other "cleanliness" issues.
Well, let's try. I just reported all the posts I mentioned in my topic, including with quoted spam. Let's see what will happen. Hope even spam aged with several years will be removed, including that in quotes.