Grr, i just typed a long reply and my browser ate it.
I just replaced the rings (middle and granny), not the der. or cranks. It works just fine, esp. since it is friction shifting. I think it would be more trouble on one of the STI-equipped bikes.
If you want to go lower than 28 (26??) you have to go to a MTB crank, and then you need a bb and maybe a der. I thought about doing this, but the snowball effect of all the stuff you need to replace made me balk at the cost.
I think you would have shifing problems if you just replaced the granny and not the middle ring.
The 520 comes with a road crank and mtb rear der, which works fine with an 11-34 9-speed cassette.
I rode across PA on one of the state-marked PA bike routes (the southernmost route), there are like 6 routes criss-crossing the state. There is a state bike coordinator (uh.... David Gordon? ??) who was REALLY helpful to me with routing, I talked to him on the phone for an hour. The state bike routes are available on line, as printable maps, and the route is very well marked by road signs. try googling "Bike PA"
PA was the scariest place I rode in the whole US in terms of traffic, and also one of the most difficult in terms of steepness of hills. It was also really beautiful and historic.
Oh yeah... and what gears you need is determined by how much crap you carry - I was fully self-supported / camping/cooking, bike weight around 80 lbs.