KJ, Tigress has it right. The Kali is significantly less rare than the Dreams items. It's almost common. As for popularity, the Kali couch waxes and wans. It's often very popular, which is why people can still get a lot for it at times, but I'm not sure if it's currently an "in" item. The Dreams items are all currently retired. I vaguely remember Yavn said they'd be released again, but one never knows with these sort of things. The Hook Chair and Dreams Turrets seem to be the most popular Dreams in my experience, but I don't know that they ever will be as sought out as the Kali couch.
Personally, I think three dreams for the Kali is too much, but it wouldn't surprise me for someone to make that trade if they had extra dreams and really wanted the Kali. It wouldn't really be a bad trade to give two dreams for a Kali. Really, one should be enough, but again, Kalis can be very popular so can be artificially inflated. Alot really depends on how much you like the items your losing and/or gaining.