I think first hand knowledge of a race track is the best feedback you can get on the enjoyability of seeing a race somewhere. I've been to MIS, Mid Ohio, Belle Isle, and Bristol. Let me tell you about them.
MIS was first. It came before Bristol. That meant when we got tickets to Bristol we treated it like MIS and tried to get tickets 60 or 70 rows up. At MIS you want tickets that are higher up because that allows you to see the entire track. You probably want to bring binoculars though to be able to follow cars that are literally a mile away on the other side of the track depending on where you're sitting. It has been about 15 years since I've been to MIS but the races are always fathers day weekend and the weekend closest to August 17th (that stands out because the 17th is my birthday). That means it is hot. There is no protection from the sun at the races at MIS.
I'm sorry but for me that is not at all enjoyable and it isn't like you can hope for rain either. Still the cars do over 200mph at the track so it is quite exciting. If Indy Car returned I'd go to a race but I'm thinking I'd take advantage of seeing cars hit 240mph at the track and sit either relatively close or in the infield and listen to the radio broadcast through the Indy Car app to better follow the race. I'm hopeful they've improved traffic flow since my last visit, but the direction we came from (north west) meant we entered the track on a 1 lane road that is about 7 miles long. The traffic backup meant it took us 4 hours to get in to the track the last time we went.
I mentioned getting seats high up at Bristol. Totally not necessary. You probably only need seats 7-10 rows up at Bristol to be able to see everything which means closer is better. The nice thing about Bristol is either a March race during the day or a night race in August means the conditions are relatively comfortable. It is a track truly worth seeing a race at.
Mid Ohio came before Belle Isle for my road course experiences. I was told to rent a golf cart for the weekend at Mid Ohio. In hindsight it might be worth it depending on the weather. If it is extremely hot you'll probably be happy you have it. You have to reserve them well in advance. Mid Ohio is probably one of the best road course venues in the US. Even though I've not been to many other tracks I'm confident I'm right about that. The spectator mounds are so well done in so many different spots on track that you can watch a race from multiple points of view. With all the on track action that usually happens on a race weekend there it is worth doing just that. Indy Car is usually there in August which is usually quite hot. There are some nice areas of shade scattered around the track to get some relief from the hot sun. The track itself does an OK job with a couple of video screens at different parts of the track as well. Still I figure I walked around the entire track 7 or 8 times the 3 days I spent there. Visiting the pit lane (literally was able to step foot right up to pit wall at a couple of spots) or the paddock area made for a really nice behind the scenes access. Totally a must if you're going to a race there to get pit access for at least one of the days. Don't bother with grandstand seats here. General admission is the way you want to go for sure. Maybe on Sunday it would be nice to have a seat in the one grandstand that might see some shade.
As for Belle Isle it was great as far as having a lot of on track action for the weekend, but the general admission grand stands were crap and the best grand stand seats aren't for sale. If you're local it is totally worth checking out on Friday and maybe Saturday, but I wouldn't waste my time on a busy Sunday again. The general admission viewing area is limited to basically 1 decent sized grand stand and one tiny grand stand. Granted one of them is in a solid passing zone, but even that is a bit disappointing when you consider the Turn 7 complex is probably the best place to sit and those grand stand seats aren't for sale. The rest of the track is covered in banners so forget about seeing it from a lawn chair. Pit lane access there is either non-existent or removed from the pit boxes a lot more than Mid Ohio. The race is in the last weekend of May/first weekend of June so temperatures could be hit or miss for hot or mild. One of the grandstands is shaded now so if I was to go that would be where I would try to get tickets. Again only on Saturday since a 3:30pm Sunday start is not on my to do list. It has been confirmed they'll have an Indy Car double header and IMSA back in 2015.