First, there is no question that the degree of knowledge and ability of bowlers has increased tremendously over the years, and it is not generally given enough credit.  As for scoring and averages take this from an old timer.  Biggest jump in scoring came when the first soft polyester balls were introduced in the mid 70's.  All increases in averages have been incremental since then, including when the resin balls came out.  What did jump radically was the amount of award scores with resin balls.  Way more 300's, but the balls blew up the pattern so fast that we didn't get as big a jump in averages as the award scores would seem to indicate. 

Only thing wrong with the game today has nothing to do with averages, but is about how quickly and badly the balls blow up the oil patterns when you have a high powered field of bowlers.  It would be better for the top tier of the game if the lane conditions forced the players to play the shot set out, rather than just burn in a pattern in no time.