Ok, first: If you want close, exciting racing, watch tin tops. Indycar is dull. Sure, the racing is sometimes close, but that's true of every spec series, and isn't something special to Indycar. Indycars are old, uninteresting, technologically decades behind the times, and the circuits they race on are mostly awful. Watch Supercars if you want close racing that is also exciting. Or watch F2 is you want close spec open wheel racing on good circuits with young up and coming superstars and not old has beens.
Indycar has been crap for a bunch of years now, and removing a heap of the downforce isn't going to make it better, it'll just make it slower. This year's Indycars are very close in ultimate lap time to the 2006 Champ Cars, which raced at a common circuit to F1 that year: The Circuit Gilles Villeneuve, which gives us a direct comparison. In 2006, the fastest Champ Car was 5.3 seconds slower than the fastest 2006 F1 car. Since this year's Indycars were setting pole laps within a couple of tenths of the old 2006 Champ Cars at the same circuits, we can safely say a current Indycar is over 5 seconds per lap slower than an 11 year old F1 car. This year's F1 pole time was 3.3 seconds faster than the 2006 pole, which means current Indycars would lap the Circuit GV close to 9 seconds per lap slower than current F1 cars.
Consider that this year is the first in a new formula for F1 which opened up a lot of avenues for development, and I'd be willing to bet F1 cars of 2018 will be at least 2 - 3 seconds per lap faster than this year's, while Indycars will be a few seconds per lap slower next year than they were this year, and we'll see a situation unfold where next year's Indycars will be approximately 13 - 15 seconds per lap slower than F1. That will put it squarely behind F2, LMP1, and Super Formula.
But more importantly, underfloor aero, contrary to popular belief among fans, is just as badly influenced by turbulence as wings are, so excuse me if I roll my eyes a little whenever I see someone claim that "ground effects" will solve everything. The fact of the matter, and one which many people don't know, is a Formula 1 car produces close to 80% of it's downforce from ground effect devices. A whopping 50%+ of the total downforce of an F1 car is produced by the floor and diffuser, with almost 30% being produced by the front wing. Both of those parts are ground effect devices, yet look at how much downforce an F1 car loses in turbulent air. Removing some downforce simply means you have less total downforce, so the net loss is less. But if you still have wings and venturis, which next year's Indycar has, then you are still driving a car which is at it's fastest in clean air, and will lose cornering performance in turbulent air. Even GP3 cars lose performance in dirty air, and they produce bugger all downforce.
As I said: I follow F1 for the technology and the innovation. I don't buy the argument that F1 needs to reduce the downforce to improve the racing, since they dramatically reduced downforce in 2014, and we saw one of the most boring seasons ever. F1 is meant to be the pinnacle of racing, the fastest, most advanced machines for pure speed. If I want to watch close races I'll watch F2, GP3, SF, Supercars, or any of the other many close spec series there are in the world. Indycar isn't a lot more interesting to me than NASCAR, the thought of which almost puts me to sleep.
Lastly, this point: "I mean, when you don't have to lift around an oval and everyone is driving the same basic car, how are they supposed to overtake or produce exciting racing?" is going to apply equally to next year's Indycar as well, since the oval spec cars have their wings trimmed to almost nothing already, so nothing will change on those circuits.