FYI, you gave him good advice if he lived in Europe. In his situation, buying DiRT 2 for $30+ instead of DiRT 3 is an idiotic decision imo. Unless he can get DiRT 2 for under $20 (not an easy feat) than he should get DiRT 3.
I agree with most of what you say, but DiRT 2 has been cheap on Steam for a long time (it's $19.99 right now). I bought the Codemasters Pack on Steam which included DiRT, DiRT 2, GRiD, and numerous other games for cheap.
In response to the thread, I think DiRT 3 is a great game. I especially love the engine sounds, and they vary from car to car. The cars included in this game are also great (especially compared to DiRT 2 which was lacking in the area). I love that you can compete in events with different eras of cars.
The rallying in DiRT 3 is better than DiRT 2 imo. The stages are realistic, but I think DiRT [1] actually still prevails in this area just because of the mass of locations/roads it had, albeit DiRT [1] is nowhere near the graphical quality of DiRT 3. The surface of the roads changes not just from race to race (even on the same track), but throughout the race as well. You'll notice when the gravel road you're on is a little rougher in places or the moistness of the fog starts to stick to the asphalt in higher elevations. The constantly changing conditions keeps you on your toes even if you think you know the track well.
I do think that DiRT 3 is a downgrade in terms of overall UI design however. The menus are not intuitive and the "tournaments" that you go to in the DiRT Tour have no sense of time and place. I much prefer the map from DiRT 2 or the Pyramid setup of DiRT [1]. DiRT 3 feels more like you're joining events randomly for no purpose.
If you haven't played any of the DiRT games and want to try them out without spending too much, you can't go wrong buying DiRT 2. If you liked DiRT 2, you'll like DiRT 3 as well.