The NS Pittsburgh Line has a distinct traffic pattern from Horseshoe Curve onto the West. Most regulars and locals call it the 2x3. It basically means that there are 2 dead/slow periods and 3 marathon periods in a normal 24hr day. It generally goes like this:
1. 20:45-01:00 is pretty heavy.
2. 01:00-04:45 is very slow, but not dead.
3. 04:45-11:45 is very fluid. If it seems like it's dying...Amtrak is close.
4. 11:45-13:00 is slower, DS might slip in some slower unit trains or position lite helpers for the fleet.
5. 13:00-20:45 sees the mail/van fleet, and uses every bit of track. The best time of day by far.
There are a ton of other places. Look around on the internet photo sites, and check out places like Cassandra, Lilly, Summerhill, South Fork, and East Conemaugh.
The trip is definitely worth it in my opinion. I've been going out there for 20 years, since I was very young. The area has a magnetism about it. The trains are just a huge bonus. For a first timer, I would highly recommend The Station Inn. Tom Davis, the owner, is a great guy, and a guru of the area's history. For the price, and the endless trackside view, you can't beat it. Make sure to partake in his breakfasts too. They're legendary to past guests.
I warn you though. Once you get there, you'll never want to leave. Even without the trains, it's a awesome place.