Well, in a way we are discussing compressibility effects. Saying that we are at a low mach number (below about .3) can be used to say that we are dealing with low speed (incompressible) flow... which was my point.

As far as the magnitude of C_L goes, think of it this way... say that we have a model designed for flight at 100 mph (flight C_L). Below this we can maintain altitude by increasing C_L, above this we can maintain altitude by decreasing C_L. So to say that induced drag goes down as speed goes up is a common way of looking at induced drag and speed's effect on it.

You can extend the argument to situations where there is a momentary high C_L (turns, etc...), but we are talking about racing (thinking flat-out speed). OTOH... that exemplifies the point.... if there will be a lot of turning (high C_L maneuvering), induced drag will be an even more important factor.... because we will be losing speed in those turns due to induced drag, not parasite drag.