Or can you trade them for caps after you've obtained them? Rather, does the bonus which comes from said magazine remain if you obtain, then later sell?

I havent actualy tried selling them but i am 99,9% sure you can do whatever you want with them after reading them and reciving the bonus. You can even build yourself magazine racks in your house and display them so they dont cluter up your inventory.

Good to know, thanks.

P.S. If anybody can confirm this it'd be appreciated.

I put mine in the magazine rack in the Red Rocket near Sanctuary and my stats were the same after. Make a save and test.