That doesn't really change my stance on it. In fact, I think it makes more sense that Watch_Dogs uses dead memes (which, surprisingly, is a term used in the same sense as the way that I use it). That's the only reason I really think it's appropriate, because it seems self aware, especially considering that this hacker is posting these in what is supposed to be a real-world reflection of Chicago.
Memes and jokes are meant to be created chemically, they're not supposed to be forced (hence why forced memes exist), and any attempts at creating memes will end horribly. If they really wanted to force something funny then they would use original content, and likely use the many dialogue outlets they have available, such as the text conversations, talking, cutscenes, etc. But it hardly seems like they were using it in that sense since Billboards are such a minute part of the game that they seem more as if they're there for fanservice rather than anything else. Initially, they spur shock in those not expecting memes so old and so dead to resurface, such as "All your base r belong to us" and "Over 9000", and later, it just becomes a test to see how far you can date yourself. I don't really see anything wrong with that, it's just a small bit of fanservice, not a means to force dated memes on people for laughs.