99% of my time is in a 172.. these days all of it is in a 172SP. I've flown up and down the east coast many times, and the biggest bang for your buck upgrade that I would highly recommend is getting your instrument ticket. Traveling 50 - 100nm, you're not likely to hit much change in the weather. I fly from the NE to SE 1 - 2 times a year, 400 - 600nm trips, and every time you are almost always guaranteed to either depart or arrive in sub-optimal conditions, or encounter them enroute. Can't do much about ice or t-storms, but those low scud days are not an obstacle when you can just file & fly.
I do dream of upgrading to a 182S, or maybe even an SR-22, but until I'm ready to commit to flying a _lot_ more than I currently do, a 172SP is the best fit for now.
edit: to clarify, I usually plan a fuel stop a little more than halfway on the longer trips. Even tho it may not save a lot of time, I'd rather have the comfort and experience of GA flying, with a nice stopover in the middle, than the pain and agony that goes with commercial flying.