If you want to make the true rally game you need to forget baja, gymkhana, rallycross etc, take a look at uk rallying. If you have a career mode start with the junior series or rally first program where you start with a micra, Toyota aygo, peugeot 107 or Citroen c1. Have a multi surface championship where you do 3 rounds on Tarmac and 3 on gravel with events like the jim Clark, the Manx, epynt, Wales gb national event. After a season of this move onto faster cars and have a 1.6 nova/corsa, mg zr, cars like that. Once the uk championship has been won move onto something like the ERC where you can use group N/S2000 or if you don't want to do global events have the older wrc cars like the 206, xsara, bug eyed impreza, accent.... Also you could still keep the older cars in a historic category where you can have escorts (mk 1 & 2), Porsche 911, manta's etc
Also for the more advanced gamers you could have a recce where you could adjust or create your own pacenotes. Also 2 shakedown session to set the car up properly, I think that an advanced set up option would be great as moving a box on a bar isn't very accurate.
Another thing dirt is missing out on is the ability to create your own graphic designs, all the games like need for speed and forza all have these features, although pre made designs are a bad idea in my book.
With reference to the stages I'd prefer longer, more techincal stages and also changeable whether conditions which actually make a difference to the handling and characteristics.
These are just my opinions but I think that the older Colin McRae games need to be modernised.