A bit of advice from someone who didn't want to give up their T4 ..... but did.
Main thing I would look at is - if you do get shot of your van, what will the replacement vehicle be? As in - how much are you willing to spend and what can you get for it?
With a 17 year old van you will know what repairs you've done, and when, and when the next cambelt is due, when the clutch/gearbox was last 'done' etc etc. If all of these are quite recent, then, if there is no rust on the important bits or expensive bits, you might choose to keep it.
I went with a quick sum of 'how much would it cost me per month to lease a new van' with the spec I wanted. If the repairs averaged more than that over a year - it was time to sell - and yes it did start costing me near that.
Also, unfortunately, my old one broke down on a day trip on my other half's birthday and that was the last time she went in it. As in - a big hint.
Also also, a couple of mechanics, a friend who was engineer, and a few other people who knew about such things kept on hinting about it was 'time'.
So - as much as I wanted to keep it - it was time.
Turns out the person who bought the van off me has had no problems with it at all and it has been 100% reliable (not that I would have wished anything else) - they emailed as they knew how upset I was at the time of sale!
One thing I will add - every time I got out of the old van after a half hour or more drive it would take me a few minutes to straighten up and be able to walk properly.
Thought I was just getting old.
Turns out, with the new van - no problem being in the driving seat for several and more hours - most comfy seat I've ever sat in.
Am I happy with the new van? Yes, but.....still miss the old tank. The new one has bells and whistles and will not last as long as the old one. It can't. Too much on it to go wrong. However, for the luxury and the comfort, it is worth it.
I did look at the Vivaros but am still waiting to hear back from the dealers after I enquired a year ago! I don't have any special affinity with VW - just these were the available vans to me at the time (and the dealer got back to me within 5 minutes when I emailed an enquiry at 10pm).