Well whe never know when such topic might get in handy in the future. Going through them __might__ ring a bell when the future I may need something related with that topic, or maybe it won't or I never will actually need it. 

But I don't actually see as a waste of resources/time as you say. It's information and it's always valuable. 

I see this mostly has a graph problem (I really do). Imagine the following:

1. Map all the information you have in a graph
1. Give weights to the edges acording to your interests in that day
1. Browse the graph in a way of maximizing your Interest 

Now if your interestes change, which they do... You can always go back to the graph or learn something else, even if you didn't even look at it the 1st time! 

The point here, is that reading the subjects helps me ~~index~~ my ideas, even if I don't read the message body. It's like reading the newspaper and only looking at the headlines. It's not a waste of time, it's actually a maximization of used time! ~~laugh~~

But that's my point of view, you're totally free to have your own!