The first step - I went through and eliminated the ones that I knew I never wanted to listen to again. This included a couple of well-remembered stinkers, several gimmicky ones (a musical, the one where you could listen to the two CDs in either order...), and a couple of ones that I have listen to very recently but didn't stand out as great. Most of these really are terrible, I can't recommend them, so they are going to get sold off.
The next (and more fun) step is to start listening to them all again! This process started last night with The Island of Lost Souls by Mark Gatiss. This is an unique piece in my collection as it is the only Doctor Who audio in my collection that is not produced by Big Finish. In fact, technically it isn't Doctor Who - it's an Adventure in Time and Space starting The Professor and Ace, who seem pretty similar to the 7th Doctor and Ace, especially since they are portrayed by the same actors. Apparently there were seven or so of these produced before the BBC stepped in and forced changes.
The Island of Lost Souls is one 60 minute CD, and all-and-all it is a fun little Doctor Who adventure. Set in Greenland during World War II, it's a pretty classic alien-threatens-isolated-group story with a little bit of WWII drama thrown in. The production quality is excellent. The acting quality is good, in fact, Sylvester McCoy is on top form here, much more like the Doctor he played than the caricature he often seems to play these days. The resolution of the plot is a bit cliche, but this is a minor criticism in the grand scheme.
It's definitely worth a listen, It doesn't look like it is available as a CD any more, although you can apparently listen for free as part of your Audible subscription on Amazon (whatever that is). Otherwise, if you want mine, you can have it for £5 including UK shipping.