There's something to be said for keeping it real. Making a movie? Keep it real. Getting interrogated by the cops? DO NOT KEEP IT REAL.
While it's obvious that a film like Iron Man requires a planet's-worth of special effects, stuff like wrecking cars usually shouldn't. We all saw how poor choice of CGI affected Ithe fourth Indiana Jones movie.
That's why it's refreshing to see that some of the fancy cars destroyed in Iron Man 2 were real. Tony Stark's Rolls-Royce getting destroyed at a race in Monaco was legit (but filmed in California).