First off, fix your air box. Turbodiesels prefer cold air, so a larger diameter intake with less bends may help (check out the discussion on Julian Edgar's articles
here). While you're at it, make sure everything is clean, well oiled, tuned up, etc.
Next, share with us
what kind of garbage is in your trunk/boot, then throw it all out. Weight savings always give better acceleration, and in all but a few circumstances better fuel economy. While you're at it remove the rear seats if you don't use them everyday. My car is also a 7-seater, so by removing all but the front seats it is 80kg lighter, which I can really feel.
BTW, does the Zafira weigh more than the Serena?
I take it that your tires are pumped up? If not, you shouldn't be surprised that it feels like you're rolling in honey.