I think you're barking up the right tree...given that you are happy with your electronics, and that you would like these to be the last speakers you ever want to buy (wouldn't that be nice!), I would buy the best speakers you can find and afford that have the sonic signature you like. Chasing cables is not the way to go, I completely disagree with anyone who sends you cable shopping given your parameters. And your turntable and CD player are fine. You don't have a big room, so unless you end up with some low-efficiency speakers I don't see the Marantz being a problem. It's the speakers...not that there's anything wrong with them, they may be perfectly fine for others, but they don't have the sonic signature you like, so find speakers that do. With your budget you have so many fantastic options, many of which have already been mentioned.
I actually like your idea of going after some 805D2, or even the 805 Diamond or 805S. They're easy to find on the secondary market, and if you didn't like them after a few months they'd be a breeze to sell. I don't know that there's another speaker on the market that's easier to sell, or that holds a larger percentage of original retail value, than the original B&W 805. You could buy a pair, listen for a year, and if you didn't love them you could resell them for what you paid or very close. Wilson Benesch Arcs are another option, more transparent and a little less boxy than the 805, but harder to find. I've been where you are, in a space that size, looking for the sonic signature you're looking for - if you liked the 805D3, I think you should go in that direction and don't be afraid of an older 805.
I actually like your idea of going after some 805D2, or even the 805 Diamond or 805S. They're easy to find on the secondary market, and if you didn't like them after a few months they'd be a breeze to sell. I don't know that there's another speaker on the market that's easier to sell, or that holds a larger percentage of original retail value, than the original B&W 805. You could buy a pair, listen for a year, and if you didn't love them you could resell them for what you paid or very close. Wilson Benesch Arcs are another option, more transparent and a little less boxy than the 805, but harder to find. I've been where you are, in a space that size, looking for the sonic signature you're looking for - if you liked the 805D3, I think you should go in that direction and don't be afraid of an older 805.