The Greyhound station in Altoona is nice enough. It is the same building as the train station. The staff is nice, and there are vending machines, a small shop, and tourist info. available.
Beware, though. Not many trains leave Altoona each day. So if one runs a little late, you may miss your connection and/or end up stuck somewhere along your trip. (I was stuck in the Chicago bus station for TWELVE hours.) So, the bus is a cheap way to trtavel, but not reliable.