Hello Kate,
I use a Grande Espace 2.2dt (Phase 3, the last but one design) so whilst it is not a true comparison to the model you are contemplating, I can confirm that my model is a fine tow car, but you do have to be particularly careful with regard to the weight limits, because of the way Renault tend to specify their load capacities.
I have owned two Espaces, and driven others, and I do find them to be comfortable, and the children like them because they are high of the ground, and have large windows. This seems to reduce problems or travel sickness.
I do agree with many of the issues already posted by others, particularly with the cost of spares, but I cannot agree with XXXXX comments about towing on wet grass, Yes it is easy to induce wheel spin, but with care it has not been a problem for me, I do not imagine it is significantly any worse than any other front wheel drive vehicle.
It is worth looking at alternatives, and there are some other makes that offer large interiors, two that instantly come to mind are the Kia Sedona and the Chrysler Voayger ( also available in the Grand version) - Even the Mercedes Vaneo. Slightly smaller, there is the Ford Galaxy and similar models from VW, and Seat. Other rivals are available for Citroen, Fiat and Peugeot.
Whilst NCAP testing results do present a way of assessing the relative crash survivability, they are far from the whole story. Suffice to say that many other recent MPV's have now archived promising and improved NCAP results, so don't be blinkered by just looking at NCAP scores.