Kind of a case by case scenario, depending on each specific piece of gear, but in general I'm a huge fan of paring down possessions, and would recommend it. Have been an on-and-off eBay member since the late nineties and got back into it again this past year to sell off things (mostly records, but a few pedals, and various odds and ends) I don't want or need anymore. This has helped me acquire a few things I do want/need.
Am also regularly in the habit of donating all kinds of stuff to the Goodwill. A big part of this is just a strategy to reduce clutter here, but the other component is that I think it's "good karma" (or something similar) to pass potentially useful things on to others. Realistically if you'll never use something, instead of having it continue to take up space and collect dust, you can let it go and someone who will benefit more from it can have it. (For a more poetic take on this, read Lewis Hyde's
The Gift: Imagination and the Erotic Life of Property, which I haven't delved into in maybe twenty years, but...it deals with the positivity in circulating things.)
As far as owning loads of guitars/basses/etc., I won't judge others exactly, but can't imagine needing more than half a dozen at a time, which is more than I've got currently.
[Edited for spelling.]