I'd say get your instrument rating without a doubt. Your commercial would depend on what you want to do in the future. If you were hoping to instruct as a hobby, then absolutely get it. Otherwise it will do you no good, other than cost a lot of money.
I left the airlines ultimately because I didn't see a future in aviation. Right now there is a large surplus of pilots and very few jobs. The hiring minimums are going WAY up and the pay is coming down. I was working as an FO for a regional carrier and I didn't make enough to pay off my student loans. The old adage of "pilots make lots of money" is long gone. It is now a long and miserable road and virtually unachievable to reach the mecca of a "Major airline". Luckily I was furloughed, so while I was away from the airline I realized what a crummy life I was living as a pilot. I realized that if I were a dentist not only could I set my own hours, be home every night, and possibly be my own boss; I could also afford to fly as a HOBBY!
Like Chemboy said, Do whatever makes you happy. If you choose aviation just go into with a sure knowledge of what it takes to succeed, and the tenacity to put up with the crappy quality of life that is required to get there. I have lots of friends that are still airline pilots, most wish they could get out but they still make it work. Quite honestly, it sounds like you are headed in the right direction.
Back to your original question. I think the skills it takes to successfully execute a precision instrument approach are very applicable to dentistry. Intense concentration, attention to detail, dealing with stress and hard decision making are some that come to mind. Good luck with school, and be sure to flaunt that license on your application.
