Well, if Finley SIMPLY kept the A's in Kansas City and didn't change his behaviors, the attendance would have been fair to middling. There was tremendous fan support for Catfish Hunter and Bert Campaneris even before they left KC in 1967; the support for Bando and Vida would have built quickly. But Finley's attitude that "this is MY team,not yours" would have depressed attendance in any situation, I think. They certainly would have drawn more fans in KC than in Oakland--as Finley acknowledged many times. He admitted that he had made a mistake in leaving KC.
I predict that fan support in Oakland will finally take off big-time now as soon as Oakland is back in the race. I predict this for three reasons. One is, it takes 40 to 50 years for a fan base to mature. The A's have now been there long enough for that to happen--and I see clear signs that it IS happening. There certainly now are the FANATIC A's fans who are keys to the market. Second, the fact that the Giants always sell out no doubt drives some marginal fans to buy tickets to Oakland games, and some of those marginal fans will develop into passionate fans.
And third, Oakland is a very different city now than it was 15 years ago. Oakland is no longer a grimy, dirty, second-rate city; it has become a vibrant, attractive city with a lot of charm. I think this will make it much easier for a lot of people to identify with the team, because the city is no longer the. . . not so nice. . .place that it used to be.