The price difference you list seems surprisingly small compared to the difference in the US. On top of that, I thought the Pilot was far more rare outside the US than the 350. The comparison really depends on what the individual person wants. A 350 Odyssey with long travel suspension will handle better than a 400 Pilot with stock suspension. So if looking purely at cost to cost, you would compare a long travel 350 to a long travel 400. Stock to stock, the 400 handles far better. If your final goal is how the Pilot handles and performances in stock form, that may be the best option. If you are going to modify either, you might as well start with the cheaper base.
I think the biggest reason people will modify a 350 is because the own one. If given the choice of having a stock 350 to ride or nothing because I could not afford a 400, I would take the 350. A year later, someone may have spent some money on maintenance of the 350. He has some more money, but not enough on top of selling the 350 to buy a Pilot. So he keeps the 350 for something to ride. He spends the money on upgrades to make riding it more fun. Another year later, he has some more money. The 350 won't sell for enough more than he paid for the previous upgrades so he still can't afford a 400 if he sells. If he had waited and saved, maybe he now could. He would have went 2 years with nothing though. So he puts more upgrades on the 350.
What is not readily available as upgrades on the 350 right now is the side panels the Pilot has, the reverse light and the dash lights. Both with long travel, and the 350 with a water cooled head, they are very similar.
