Ahh, I think I can go 2 for 4 on this one.
1) No idea, I have never tried. It also seems like there may be more room on the md80s between seats than the dc9s but I am not sure. Sorry, answer to this one sucks.
2) In terms of other airlines, I have flown Northwest once and Delta once and I cannot remember to be honest. So that is two strikes.
3) An easy one. Being a frequent flyer is free, you really don't get any added perks except for the miles. In the past they have had double mile promotions and they for a long time and still do have a promo where if you book online you get 500 bonus miles which do add up. Also they have some deal with a creditcard maybe, but I am 100% they have a deal with a long distance carrier where you get miles for money you spend with them, but I don't do any of that, just the miles from flying and online booking. Free ticket anywhere they fly at 20k miles seems pretty good, i'm almost there just above 15k I think. Seems a good deal.
4) This is hard to say. When I first started flying them winter of 99 and early 2000, their flights on dc9s were rarely even 3/4 full. The back 1/4 of the plane would usually be empty so there were many seats you could move to to have no one next to you. In the summers I am afraid they are booked pretty solid. That is why MKE-BOS throws the md80s in that route during the summer, due to demand. The 6am flights usually have more room than the 7pm flights, they are booked pretty solid around the summer time and holidays.
They really are amazing, did you catch the NBC Dateline undercover story they did? They flew the same route the same time the same day one undercover person on Delta and one on Midwest Express. They said stuff about the leather seats and the REAL china plates and silverware and free wine, but the thing that struck me is that they said on the Delta flight they only saw the flight attendant ONCE and that was to give them a snack. On the Midwest Express flight the F/A came around SEVEN times to offer the food, wine, other drinks, cookies, coffee, tea etc.
It really is like first class I suppose. My first commercial flight EVER I flew Midwest Express and I was like "man, airlines have such a bad rap, this is luxury!" Turns out I just got lucky being on a Midwest Express for my first flight as later I did fly one Northwest flight and one Delta flight and it was absolute trash.
One thing that really stands out in my mind also is that the flight attendants never EVER go around and pick something up in a TRASH BAG. Always they have a cart, or a small bin, or they will just pick it up from your hands. I think this is very classy and when I saw this on Northwest and Delta I really realized that I did have luxury on Midwest Express.
Hmm what else...One time I had an 11am flight BOS-MKE cancelled because the plane had a mechanical problem. They got another plane for about a 1pm departure, everyone was sitting on the plane when the pilot came on the speaker " Well folks, there is no easy way to really tell you this, but this plane isn't going to get off the ground, I did my preflight check of the exterior of the aircraft and the blablha(i forget)has a problem and we aren't going to fly this aircraft" So everyone got off the plane and were in the terminal at the gate making other arangements when the flight attendants brought our meals out into the terminal, and also bought clam chowder from Legal Sea Foods and served us in the terminal. Show me another airline that will do that.
I guess that is it for now, man I am going to get carpel tunnel from typing so much.