I actually own both, the 1VJ 600 and an 08 Ten. I would agree that I would not sell the 1VJ for any reason. But lets get one thing clear. The 1VJ was extremely unreliable and died from overheating on a massive scale. That happens when designers care more about looks than they should do. Relatively easy fixes which Yamaha incorporated in the 3AJ. And carried on into the old 660Z's.
My Ten is fitted with a Kev O2 Eliminator and it has turned it into a delightfully smooth ride. Still no patch on the old Ten's carbed engine. Especially at low speeds where you don't need the clutch, the thing doesn't stall. When i rode an old 660XTZ she felt just the same. Smooth.
Weightwise the two are not that far appart. Although the old girl is far easier to handle.
Seat hight is about the same. Both need tiptoes. The old 660XTZ is better but not really for off road anymore. The 600's soft long travel suspension needs firming but then its great. Try it off road!!
Who needs watercooling if the engine doesn't overheat? With a few simple mods i admit. But modern regulations demand it.
The seat is a certain step back. Not that the seat on the old Tens was all that great.
On the whole the new Ten is a very different bike to the previous 600 and 660Tens. Modern. With all the gimmicks and comforts you expect nowadays (except the seat maybe)
The old bikes are for real men who need to fiddle with chokes to start a cold engine, who ignore the e-starter to show off how strong their right leg really is, who need to pull the brake levers all the way to the handlebar and still not blocking the wheel just to avoid crashing into the back of the car in front, who need to keep the revs over 4500 to keep moving with the modern traffic, who don't need a power outlet as it will drain the battery faster than it can recharge it. There is a word for that: Nostalgia
I really love the old Ten to bits as it has real character but in the modern world the new Ten rules. Still I will probably sell her next spring and will be sad to see her go, but go she will.
By the way, the 1VJ was rather expensive when new in 86, so much so I could not affort one at the time. I had a 550 instead. Her engine was so eager to rev and sooo smooth. In many ways the XT engines that followed were a step back.
A bit of my experience only. I have owned or ridden them all.

Rob