It used to be frowned upon back years ago but now, people are more tolerant with it. But bumping old news threads is still a big no-no though, unless it's something that can make it become "latest news" again.
One problem with it is when you bump a long thread with outdated information or opinions, and then, these opinions are the first things people see. I see this on some admin sites from time to time, particularly with SEO advice.
I cannot tell you the number of times I've seen outdated 2004 advice here on FP and it can be it's own brand of annoying, as people will go out armed with that knowledge and will parrot it all over the place lol
A few myths:
Meta keywords matter - Google doesn't care.
PHP is fast and efficient - It's really a snail.
People use SEO URLs just because Google likes it - Google doesn't care, you use SEO URLs because it's professional (a .php or .anything in a URL makes it look dated at best and extremely amateurish at worst) and the names in the URLs give people hints about what they're about to get.
If a company makes a lot of money, it means the people are competent, hence we should take their vague opinions as gospel - I wish, but no.
Linkbacks are important - Yes and no. It isn't really as important in the ways you think, but it can help guide organic users.
vB was good before IB ruined it - I have actually used vB. It was a horrible, horrible software. They hid setting manager navigations under drop-downs, used frames which didn't work on mobile, had permissions for every little thing, had an amateurish looking control panel in contrast to the competition and piled on 30 disjoint features.
Plus, I had mods just casually finding security vulnerabilities in the thing.
I remember MyBB's control panel actually looking quite reasonable at the time compared to the frame infested one. Many of the problems people now see in hindsight and chalk up to "it was normal for the time" were things I was pretty annoyed about.
I can go on but there are quite a few myths I see on admin sites.