Hi BongoBongo. Welcome to the forum. When it comes to the value of any given model, it really comes down to the person. Do you think it is worth it?
As someone who appreciates vintage gear, IMO...it is a neat piece. I am not much into TV's in my boxes but that is merely subjective and my personal opinion. On the plus side, more switches buttons and doo-dads are always a plus in my book. The fact that it is a JVC is another in my personal opinion. It looks cool because it reminds me of a JVC RC-M70JW on steroids. Based on my experience I will say that JVC, Panasonic (and it's affiliates) are known to have decent sound and quality however, speaking for myself, I have not personally heard this model. My guess is, properly working, it should sound nice. Especially since it has a deeper cabinet due to the CRT.
I will not say to purchase or not. Use your gut feeling. Ask lots of questions on condition and find out if the seller can confirm proper operation of the TV (if that is important to you) among all features. How about the tuner, dial lights, speakers, etc.. I would imagine this box is loaded with circuitry as high voltage fly-back circuitry is required for proper CRT operation. As with any vintage box, things can and eventually do fail.
I am going to assume here so bear with me. By asking the question, it sounds to me as if you like the box and would pay the price currently offered if you could guarantee that everything works properly and the box is sound. Am I reading you correctly? If so...ask yourself, if I pay $510 dollars for this box "working", am I prepared to receive a box for half a grand only to have it malfunction after a week of ownership and usage? How would I feel about that if it were to happen? Do I trust the seller? Am I willing to take the gamble? Do I feel comfortable with the purchase? Is my wife going to kill me?.....etc..
If after reading this, whether you feel comfortable or uncomfortable with the purchase, I think you have answered your own question
Edit: If this is not a Buy it now...expect the price to go higher than currently listed....just an observation