Yes, beauty, and value are definitely in the eye of the beholder, so price can vary somewhat. Of course the market can vary also. You may be willing to part with whatever, and someone else may be willing to part with more.
I owned a new 4400 back in the '70's ($1200) I'd say personally, that it wasn't the prettiest of all the Marantz's, as IMO, the square buttons detracted from it's look versus other Marantz gear of the time, (I liked the round buttons on thier other equipment better) but it was still quite attractive none the less, particularly all lit up, with the CRT dancing away.
Certainly had lots of bells, and whistles, and the only reason I can see owning, or I should say "needing" one today, is if you own lots of 4-channel media (Quad Tapes-CD-4, and SQ LPs) Output in Quad was I believe rated at 50wpc, not 60wpc, and a "supposed" 125wpc bridged to Stereo Mode (Trivial I know, sorry)
Opinions on price of course cannot be firmly nailed down, but I suspect if the unit is absolutely flawless in every way, including Cabinet, I'd say possibly $800-$900 tops as a realistic value. Yes, I'm sure there's those who'd exceed it's new retail price, just to say they have it, and you don't. (bidding wars) lol
The CRT was in a way a gimmick, and certainly didn't add anything to the 4400's sound quality, or the precision of it's FM Tuner. It was more "eye candy" than anything else. (Although I sure wouldn't mind having myself a Day-Sequerra Tuner!) Have one burn out, and you'll need lots of luck trying to find another.
Years ago, I seen a slew of these CRT's come up on ebay, but that's long gone. Maybe about the only way now, is by buying another comparable unit, and cannibalizing it for parts. The shame is, if the CRT was "only" for sound field display, it wouldn't be a problem, but it's also used for FM signal strength, center channel tuning, and multipath distortion. Once it goes out, it compromises one's ability to properly tune FM Stations. You'll have to guess then "by ear".
If you don't have any 4-channel media, or 4 speakers and solely play 2-channel, I'd seriously consider something else. Mark