At least for 1979, says there were 20 auto-bids.

http://en.wikipedia.org/wiki/1978%E2%80%9379_NCAA_Division_I_men%27s_basketball_season

For 40 slots. That means to get into the top 40 (single digit seed), there were 20 at large spaces available.

Today there are 34 auto-bids for 68 spots (still half), and of those 34 auto-bids, typically somewhere around 15-20 are true NCAA quality teams, with the rest being the 13-16 seeds in the tourney. So the teams that receive seeds 20-40 (overall) are still mostly at-large.

Not sure how quickly conferences start adding up from 20 to 34, so your point may be valid for later years.

It's always hard to compare across eras, b/c variables change. The game is different (3 point line), the overall competitiveness is increased IMO with so many more kids specializing, playing AAU from 3rd grade on, etc., and the money and scrutiny is intensified.

Did the best I could to try and pull enough metrics to get a decent sense for when we've been the best. I don't see a 10 year stretch in the last 60 that could make a case above the current one.