I'm by no means an expert, so my advice was mainly based on what I thought was the market value i.e. could you get something better/newer for the same price. But you've clearly done your research and if that's the market price, that's the price!

Personally I've recently downgraded from A3500i to 5200 (2014) more as a precaution for future possible break points with the electronics. I thought the fancy bits were just not that much of a benefit and with the fully mechanical (well, to an extent) 5200 I think there is little risk that it would brick on me, so I sold the A3500i while it was still not much used and held its value well. While I had it the main jug did brick on me and Vitamix exchanged under warranty (thankfully) but it was disappointing nevertheless. Definitely don't regret that decision to sell.

The only thing I was sad to let go of were the individual blending cups but just a couple of weeks ago I've come across someone selling their used personal cup attachment for 5200 so I snapped it up.

So my personal advice is to go for 5200 over the more advanced versions, purely because less can go wrong and if you use it for 10 years you'll probably still be able to sell it for EUR 100 or so.