I've recently become the proud owner of a '80 4001 in Azure Glo. I played loads of them before I settled on this one. I've not come across a bass that has so much variation in build quality and shape. Some were right old dogs, but luckily mine has the best neck of any bass I've ever played, beautifully slim and fast, It's just right for me.
The bridge was hard work though. The saddles kept moving in the tail piece and because I'm a pick-playing palm muter the bridge was essentially useless and I've changed it for a Hipshot. plus my pick kept getting caught in the treble surround, so that came off and a Pickguardian (excellent service) went on.
My advice would be to try as many as you can and find the one that fits. I love the style, the tone and everything. Sure it's not a 100% ergonomic instrument, but I find it a lot of fun. I thought some of the brand new 4003's I played were excellent and would've bought one had I not got my 4001 for such a great price with blind luck.
Yes, the output is not massive, but that's what your gain knob is for, plus you can't beat them through a bit of valve!