I think I've said this before, but I used to hate the 4000 - I thought it looked weird without the neck pickup - but I changed my mind when I saw the video of Stanley Clarke playing one with Return to Forever before he started using Alembics.
I just played a 4000 the other day - I attended the first "(San Francisco) Bay Area Rickenbacker Confluence" (or BARC - the other name choice was "Bay Area Ric Festival" but that would be BARF) the other day and someone had an early '70s 4000. I brought my amp in to compare the sounds and it had a nice growly sound. Here's a (bad) pic of it, next to my 4001 and someone else's 4001S:
Next time we do something like this I want to record the different basses for comparison.
Oh, and +1 to the relatively fair pricing...