There are two reasons I can think of not to get it:
One is, as you pointed out, there's a possibility that it will date the car down the road, but it's features will still operate as they did when the car was the latest and greatest so I'm not sure that's really much of an issue.
Once it's an older generation M3 it will always be considered either dated or classic regardless of whether it has iDrive or not right?
The other reason would be simply to lower the price of the car a bit.
If you have never owned a BMW with iDrive then I don't believe you would miss it one bit, but if you have owned a BMW equipped with iDrive and gotten used to the access and enhanced control it gives you then you would most likely miss it quite a bit.
After owning a few iDrive equipped cars I bought a used E92 335i on a whim. I didn't keep it long, but I loved everything about it except the fact that it didn't have iDrive. trying to access everything through the MFD was a nightmare after being used to iDrive which gives you access to far more options and is easier to use than the stalk/MFD (especially while driving).
Definitely spend some time playing with iDrive at the dealership and see if you think you'd miss it before making such an expensive decision.
2011 E90 ///M3 DCT ZCP | Space Gray | Silver Novillo |
2011 F10 550i | Space Gray | Oyster & Black Nappa | ///M Sport | 8 Spd Auto
"A toast then: To the BMW M3, the greatest all-around car in the world."
-Arthur St. Antoine, Motor Trend Magazine's Editor at Large