Generally, you can identify a wothy thread the one that has many replies. Additionally if you see big activity - many replies in short period - that definetly means there's something going on in there!
If it's a thread that is on the top and have small numer of replies - if you have the time to check it and it have an interesting title - why not?
Many of the questions in the LL section are addressed to a LL owner - a review question. I check the sites only of people that have history in the board and have taken part of some of my personal threads or have said something interesting... means people that got my attention
Good threads are also general questions where you can see that the first or some of the first replies are from persons that have your attention.
Subscribe for threads that you're interested in, that's a good way to save time on READING the thread itself (the one that you're interested in). That helps you not look at the board. A good thing is to have the page opened all the time, if you can stand not looking at it all the time of course
Don't open all boards all the time - stay in the one you're generally interested in. If you find it boring - move to another board that you find more useful. Tomorrow come back at your favourite board, check to see if you missed something (threads with many replies for instance).
Hope this was useful
Andrew