Being an Indy resident, here are some thoughts to help with the sold-out block situation.
Indy is home to (you guessed it) the Indianapolis 500, where we show every city for nearly 100 years how to move 250,000 people in and out of a small section of town in just a few hours.
(And some people thought we couldn't host a Super Bowl.
Right...) Because of the race, we have many hotels, just not necessarily as close to downtown to allow you to walk.
Use whatever hotel resources to search for hotels along our interstate system, specifically I-70 East/West, the I-465 loop around the city, and I-65 North/South. If you happen to drive to town, it should be very easy to get hotels within 3-10 miles of downtown. Flyers who are getting rental cars and have just yourself and 1-2 people might start with the hotels around the Indianapolis International Airport. Drivers should look to the airport area hotels and work yourselves east along I-70.
For larger groups that drive or have multiple cars, a favorite hotel that is VERY geek-compatible, being hosts to two annual local SF conventions, is the
Indianapolis Marriott East, about 15 min east from downtown on a straight shot, directly next to I-70. It's been recently renovated. Plenty of restraurants nearby and a Starbucks, too. Right next door and sharing the same parking, also a Marriott hotel, is a La Quinta hotel with cheaper rates, with the bonus of being able to use the next door Marriott's pool and other resources if staying there.
I took in GenCon for a night last year, enjoying several inner celebrities in our fandom as well as meeting Tolero and Producer Glin. I hope to repeat this fun this summer.