First of all, keep this thing in mind that your Vezel is 4WD, therefore, it is not possible to get the fuel average as good as 2WD and I think the average you're getting from your 4WD Vezel is okay. Messing with it may result in even the worst average.
Secondly, other than just making your ride feel a little lighter, there's nothing much you can expect from changing the air filter to a genuine one, it will not make much effect on the fuel average of your ride.
The rest is your choice.
I hope it helps.