RENAULT-forum

First of all sorry for using English.

Anyway - I wouldn't buy an used Espace V from the beginning of its production or a demo.
There were too many teething problems with those cars that were only resolved recently in production. Every Espace forum in FR, DE, PL is filled with customers that replaced it by another car or a new Espace. Most of those negative experiences you've read are tied to those first cars.
After all there's a reason that original owners want to sell them after a year of usage.
As for the diesel vs petrol - these are similar in day-to-day performance except that gasoline has a lot less reach on one tank and new 7-box gearbox from Getrag that is still receiving firmware updates.
Personally I use petrol version (07/16) and I'm satisfied with it. My average fuel consumption is around 10L/100, that includes packed city with lots of traffic jams and motorway (140+).
"On the road" (pretty much constant 70-90) it goes down to 7.5-8/100.

Best regards