But in order to be a reliable predictor, I think it would be necessary to predict the economy as well. The same startup that would be successful during the bubble would not be so successful after it popped. In other words, I don't think they have enough inputs to be reliable predictors.

On the other hand, perhaps they don't need to be reliable absolute predictors. The VC's question is basically which should be funded. This might be able to give a rough ordering, which is plenty valuable.