Okay, my 2 cents worth. I was consistent in the 175 - 185 average for about 8 years with a high of 194 3 years ago. I have accumulated bowling equipment through pro ams and a few purchases.
About 2 - 3 years ago my average began to slip. Do I get rid of a ball every time my average drops? I did go an get a coach, unfortuantely due to reworking my game my average dropped to 167 this year. Now, do I pick one ball and use it exclusively until the average goes back up?
Yes, I am being a bit of a smart A, but in answer to the original question, I agree with the idea of average not being the determining factor. If a bowler has the basics and wants another ball or two, go for it. I also agree coaching is money better spent while learning. A good coach will spot the flaws you are not aware of in your game. Also a good coach will assist you in determining the need for additional equipment.
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"I cannot change the direction of the wind but I can adjust my sails to reach my destination." Jimmy Dean