If I was in your shoes I would definitely go DO. Gunning for uber competitive specialities is really the only problem with going DO, not that it can't be done because it is all the time (watch me get flamed for this last sentence). To answer your questions:
1. I have no idea if your scores will go up or not. I guess it depends on how hard you studied this time around, and how hard will you study for the next time around. Admission to medical school is always competitive, and current trends show competitivenes to increase with admssion slots remaining status quo. However, AMA (MD programs) want to dramatically increase enrollment, and there are at least 5 new DO schools set to open within the next few years. This should stabilize competition, but only time will tell.
2. IMO every DO school is a good scool since every school will allow you to pursue your dream. Currently there is only NYCOM, but apparently Touro-Harlem (branch campus of Touro) will be opening for first year students in 2007 (this years admission cycle). I am a NY guy myself so I am a little excited about this.
3. As far as tuition goes:
http://www.aacom.org/colleges/tuition.asp
I think that you are under the conception that there is some type of weird stigma that is attached to the DO degree (you said, "it doesn't sound too bad to become a DO"). I used to believe this myself. I am currently shadowing a DO in a VERY competitive specialty (one of the ROAD to happiness specialties) and he has patients lined up like you wouldn't believe. On an office day the guy sees about 100 patients and he is dam good at what he does! Trust me, you will not have to explain to patients what the difference is between an MD and a DO like some people may tell you. Most people could care less what two letters are behind your name as long as you are good at what you do. I encourage you to find a DO to shadow for a few days. You will feel better about your decision to apply DO.
Use this website to help locate a DO:
http://www.osteopathic.org/directory.cfm
Good luck

!