Yes ... absolutely. There are about 350,000 who attend the event and numerous millions who watch. I read an article yesterday that gave some statistics compared to other major sporting events and they were pretty impressive.
-More people than attended the last four Super Bowls — combined. It's almost five times bigger than Indy's Super Bowl.
-Nearly twice as many people as attended the record-breaking 2015 Kentucky Derby.
-Over 100,000 people more than attended all the games of the 2015 World Series.
-More than double the attendance of the last-reported Daytona 500 attendance in 2012.
-On Sunday, one person out of every 1,000 people in the U.S. will be at the Indy 500.
The Daytona numbers are skewed because that was a bad year for travel when gas was upwards to $5 a gallon. I think I heard they had 250,000 this past year in the new stadium but either way ... the Indy 500 is still a big, big deal. Anytime you can reach speeds of 230 MPH people are going to want to watch!
I think it's still a major event, but not what it was back in the 70's. NASCAR has taken the popularity away from the open wheel racing segment. As to your discussion of attendance, sure more people attend BUT that's only because it has that much more capacity. I'm sure if you added in television viewing the Super Bowl would blow away the Indy 500, as would the Daytona 500.