I think that the breds are a more risky investment. With feeders or fat cattle or pigs, corn.... you can buy futures, hedges... to guarantee a price. Unless you have a buyer locked up at a given price you can't guarantee anything with breeding heifers. I've had three operations that I know try to do this in the last couple years try this and all 3 got burned. One was bad timing, one was bad weather (no rain=no grass=no market for cows) and one was bad luck.
Now with all that doom and gloom, if you're not going to have much in them I see no reason not to take a shot. The national cow herd is small, when this economy turns people are going to be wanting higher quality meat products and that should in turn make the fats worth more=feeders worth more=breeding females worth more. One thing that I would look at is, if you can't get the price that you want can you make cows out of them yourself? Do you have the feed, facilities, time and motivation to add calving 30 first calf heifers?