I'm in six, as into it as ever. Four playoff contenders that require the normal amount of oversight, one true tear down rebuild that requires less work but a more active attempt to find trades that help, and two "ideal" situations, leagues where I love my rosters and they're mostly just in a holding pattern until something goes wrong. I also play in extremely deep roster leagues so waivers don't require much work in comparison to some peoples' leagues...there's nothing out there.
I personally talk general dynasty strategy/philosophy less because I've got mine figured out and it fits well with the direction the NFL is heading. Not much to talk about really and the vast majority of my "dynasty time" is now spent looking for trades and chatting in my leagues, whereas in the past a lot of that time went to researching and discussing dynasty itself, as a format, on a board like this.
I think eventually you hit a comfort level as an owner, if you're any good at this. And then all that needs to be done is you adapt to new trends and swap out past player knowledge with present player knowledge continuously. You spend much less time actually talking about dynasty when you feel you have a good foundation, and then your philosophy just needs to be applied in each individual league, and that's where the majority of your time goes.
I'm lucky. Out of my six dynasties, two great commishes run four of them, and I run the other two. So if there are openings, only a great owner that has already been vetted and is probably already known to someone in the league gets in. When you have a stable league due to good commishing and competent replacement owners, it basically runs itself.
Friendships and rivalries develop over time, and people become invested in winning outside of the payouts. That's what makes it fun. Right now I'm in a league with a guy who mails every owner he beats a package of gummy penises along with a message about how they've been served their "bowl of dicks". I have a league where we do Game of the Week interviews, with a rotating schedule allowing that weeks interviewer to ask questions of the owners in the matchup he's most interested in. A couple of them are Devy leagues. I have another league where we draft rookies before the NFL draft--for a few years now we've been posting the draft on DLF so they can follow along (as it's pretty much the first draft of the year every year) and we get 6-8 pages of strangers chatting with us about our picks and our draft, which is pretty cool.
It's all about getting the right group of owners, and then any league is usually a blast, whether you're competing or rebuilding or whatever. I'm lucky to have worked my way into a pretty large network of great, knowledgeable dynasty owners and we always pull from that pool.