Is it work 20k? no. - maybe 15k? yes. Its agility, speed and larger cargo hold than the light and med ships is worth extra cost - I just couldn't justify 20k worth the cost. If it was 15k - I'd probably own one (I do a lot of alone sailing - and though my War Frigate is still #1 in my books I'd love to have a War Sloop for runs).
I guess its my mindset - if I get to 20k I now see it as 'half way to a War Gal and the 16 cargo hold... so if it was a bit cheaper - I'd scoop one up
My dabloon worth I guess