My iPhone 4s had quite some issues, broken lock button, a dock connector stuck in dock mode (thinking that it is in a music dock constantly) and my battery wasn't the freshest either after almost two years. So I decided to give it a polish and replace the dock connector the power and sensor cable (to fix the lock button) and a new battery.
Repair went quite well, dock connector and battery replacement are fairly easy. I was sweating a bit with the power and sensor cable, a third or fourth hand would definitely have been useful here and there. But it went well, except that now the auto-brightness function doesn't work anymore, must have something to to with the sensor that maybe doesn't sit 100% correctly... But I am happy about the "new" phone.
Take a piece of paper, orden the screws and parts you take out the phone and write next to them in which step you used them. Definitely helps for the more complicated repairs.