The Lada Niva is a cool idea as it's part of Dakar history, and you may touch some more customers is you offer a road car transkit too, but you may touch less customers than with rally theme.
I would buy a Lada Niva is you do it, but which version to choose...? there even was a prototype with larger drivetrains (1986 or 87).
I have some pictures from dakar that can help if you need.
The 106 Maxi would be one of the coolest idea but I really think the 205 Evo2 is on the top for most of us, and we have a base to start from and I personaly have tons of pics !!