Other than that, it remains a great resource and I use it on a daily basis.
Preventing dilution and keeping focus was one important point. One consequence was being rigorous with off-topic questions, the founding of the "sister sites" (first the Trilogy SO, SF and SU then StackExchange) was another.
There was much debate about what should be considered on-topic and off-topic back then. I remember the discussion about HTML and LaTeX quite vividly[1].
All of this discussion was terribly tiring but on the other hand it was good because SO was different from other communities in the sense that people tried to stay focused.
I think there is still good intention behind the strictness, but I agree that the execution leaves a lot to be desired.
[1] http://meta.stackexchange.com/questions/12918/can-we-have-a-...
There is a reason SO has excellent results on Google - the content is carefully curated so that it's timeless, and editing allows it to get updated where it needs to be. Yes, sometimes good (at the time) content gets discarded, but that's the nature of it.
If you want that kind of stuff, do it somewhere more transient.
If cleaning up irrelevant questions can't be automated, how about having a "this is no longer relevant" button appear a few months after the post has been answered? Or having a [subjective] tag that has an expiration date on being indexed on Google.
Now that the bad ideas are out of the way, let's hear some others.
Trying to make SO a jack of all trades will degrade the quality of the content and make the site worse - the whole reason that it's the good source of content it is is because of these restrictions.