Definitely convert them, if for no other reason than to get a digital copy before the cassette starts to degrade due to poor storage or over use (in the future, that is). It doesn't hurt to make them available for trade, as someone previously mentioned, maybe it will prod the taper to release a digital master. As someone who primarily collects recordings from the late 60's/early '70s, I've heard of more than one collection of masters that were destroyed in house fires, thrown out (yep, taper passed away and clueless children put all the reels out at the curb), or destroyed by flood. If as many people as possible archive whatever generation they have, it guarantees that performance will live on for many years to come.