ShoeIn,

Average Prizemoney is not an indicator of class on it's own, however, combined with other factors it is extremely powerful.

Couple of suggestions -

Look at the beaten margin, not the finishing position.
Consider the previous race prizemoney in comparison to today's race prizemoney.
The number of days break is more of a guide to fitness combined with beaten margin.
Get yourself a database, either pay for one or build one youself, so you can test the importance of various theories. You'll be amazed at what shows up, and what traditional theories are just plain rubbish.

Trash 3 year old races and horses - generally they are under the odds and fail to perform unless you are extremely selective. This is usually due to hype as 2yo's.

HTH.