Well, you could buy the 300, and get City Navigator, in lieu of the topo maps that are included in the 400t. High price aside, remember that a handheld GPSr is not geared towards those that want a car routing unit. You can get that in a Garmin Nuvi for $200 elsewhere.
I know what you are saying and I contemplated buying the 300 but I do want the topo maps the 400t has. I just thought that I could ocassionally used the GPS for auto navigation without having to add another set of maps. I am mainly going to use the Colorado for paragliding and as far as it calculates Glide Ratio and Glide Ratio to Destination (which it does) I guess I just have to settle for no auto navigation.