If you are happy with your current car then you need a better reason to change it than your car dealer wants to shift some 'difficult' cars your way!
You say your 02 Scenic has been very reliable, I can confirm my 02 is too! Look around the forum & you will see endless problems reported with the later,
version of the 1.6 16V engine - Renault seem to have made it worse not better since 2002! After the Scenic facelift, sometime late 06, reliability is claimed to have improved, but more time will tell.
You say you want something a bit more economical - I doubt an 06 Grand Scenic 1.6
will be measurably more economical than your old 02 Scenic - its heavier for a start...
And another thing....
YES - you can sit 7 people in a Grand Scenic (well 5 people & 2x 7 year-olds or smaller)
there is a price
The middle row of seats seem to have been moved forward (to give some legroom to the rear row?) compared to the 'normal' Scenic - so 95% of the time, when you DON'T have 7 people in the car, the kids in the middle row get a raw deal leg-room-wise.
When the back row of seats are stowed in the boot (i.e. most of the time!) not only do you get a higher floor in the boot but also no spare wheel as there is nowhere to put it!
Ever wondered why 3 year old Grand Scenics seem to be the same price as normal Scenics the same age? Now you know!! - they weren't the same price when new though
My advice: since you like your current car so much & expect reliability, you need a good reason to change it. Why not wait until your current finance agreement ends with your old car? At that point you will be free to look around ANYWHERE for a replacement. By then you could probably afford a facelift (06/07) Scenic with, say, the 1.5 Diesel which appears to be a much more attractive, reliable proposition, & is significantly more economical than your old car??