I went to the one in Kansas City. We went to day one only, and it was packed. But it was awesome to see the spectacle and be a part of it.
As far as day three, I think that would be good. You will get a sense of the scale of what the NFL puts on, but I'm guessing you won't get the juice of what day one feels like.
If you do decide to go on day one, I would recommend getting there early. We got there about 1:00. There were people there but no packed yet. So we had relatively short lines to get food, beers, and really walk around the grounds. We could walk right up to the front stage area. That draft theater is MASSIVE.
We then staked out a spot in front of the big monitors they put up to watch the draft. When you are farther out we had plenty of room to move around, but as it got closer to draft time it got busier to get beer and food.
The bathrooms, however, were a joy. They brought in full flushable portapotties. There were attendants everywhere keeping things clean and I never waited to have to use the restroom. They had tons of these. Not sure if that was just a KC thing but it was memorable how clean and quick that process went.
If you do go on day one I would bring a blanket or something to sit out as you wait for the draft to start. During the afternoon after we ate we just sat on that blanket and drank beer and people watched. It was great.
On a side note, where are you up here in Wisconsin? I moved up here last year and live near the Tomahawk area. If I hadn't gone to the KC draft I would have gone this year.