I live here and avoid downtown at all costs during the F1 weekend. Not only will there be a ton of people but there will be traffic problems due to the number of closed streets. Off of my memory the closed streets were 2nd, 3rd, and 4th streets between Congress and Lavaca.
Expect all the popular restaurants within a 5 mile radius of downtown to be even more slammed then they usually are. Expect wait times to double.
If you are staying downtown it might be fun but just plan for the crowds and you should be ok. Also if you wanted to try the food truck scene I would expect for a lot of them to not be in their normal locations so if there are any specific ones you wanted to try then make sure they are there and often the only way to do that is check their facebook page.
Oh and I still think it is crowded even when people are at the track. I know several people who take their kids downtown to look at the cars etc... but don't go to the track so expect increased traffic even when the race is in progress.