It's all about the post count, man.
I wouldn't let the last few months color your opinion of pre-allo. While I agree that it was more valuable in the past, we're also in the middle of the summer, which seems to cause a huge influx of *****s that do nothing but start stupid threads and intentionally troll (something you're obviously aware of). The amount of trolling and stupid posts is getting on my nerves too.
I think to some extent SDN is approaching maturity. There's so much information in the forum that, with some time spent searching, you can almost assuredly find the answer to any question you have. The problem is that 1) the material isn't organized well (i.e., you have to search for it, and the BB search algorithm is absolutely horrible) and 2) people refuse to search for it (something I've mentioned before).
Something that I wanted to do was create a pre-allo "quick start" guide - a collection of links organized by individual questions that new users could either check out on their own or be referred to when they post dumb threads. Unfortunately I never got around to it because I ran out of time, but I'll start a thread and see where it goes. If something like that was updated every once and a while and stickied, I think that would make the forum infinitely more helpful and cut down on the chaff.
I think the especially veteran users are clamoring for a time when SDN was perhaps a smaller community that was much more... professional might be the word? Unfortunately with growth you see an increase in both users that contribute and users that bring the forum down. While there might be an increase in the amount of crap that has come to the community, I would bet big money that there's also been in an increase in the number of members that contribute very helpful content.
As for the images with no text... well, I'm one of the bigger offenders there. I just find them hilarious. I've noticed that most of the times when those images are posted (by me or anyone else) they're posted in a thread that we all know is going nowhere. That doesn't excuse the behavior - and if the goal is to make the standard of behavior significantly more professional than this would have to be done with altogether - but it's not as if legitimately useful threads or threads that ask decent questions are being derailed. In other words, yes, there's stupid stuff that gets posted, but I don't think that it interferes with the more legitimate and useful part of the site.