Well, these may be a bit bigger than "small things" but hey!
- Full race weekends ( "Friday Practice", Quali, Warm up, Race)
- Better pit-stop strategies (choose start-fuel, number of stops)
- Fully animated pit-stops, GT4 style.
- Custom bodyparts; there are never enough, and the Forza ones are repetitive
- Animated/ detailed "Garage" during race weekends
- Be able to put race-car engines in road cars
- Proper "Buy and Sell"; haggle prices etc.
That's enough for me. Some of your ideas are great aswell, I especially like the "Crate Engines" idea.