Limit suspension travel to half of what it is now, limit tire grip by decreasing with and softness, drop the engine redtrictor so You get higher revs, and make the regulation in favour of multi cylindre naturaly aspirated with no silencers on the stages.
Rally has to look, sound and smell fast.
And last but not least, make the TV coverage much better (give it to Eurosport).
If You can couple this with an online/PS4 rally simulator based on the physics of Richard Burns Rally where fa
ns can play against their heroes in real time, I think You have a winner