Slowpoke, thank you so much for all your advice. I had an amazing weekend trip thanks to your help!
For anyone else who stumbles across this looking for info, here's what I ended up doing:
I stayed in Valley Hostel in Lauterbrunnen. It was a good price, clean, and the staff was friendly. If you're planning on staying overnight in the area, I would *definitely* recommend staying in a hostel or hotel in one of the valleys as opposed to staying in Interlaken iteself. The setting is just so much more beautiful, and I didn't find Interlaken itself to be all that interesting.
I arrived in Lauterbrunnen ~9.00 Friday, dropped some of my stuff off at the hostel (it was too early to check in, but I was allowed to use the storeroom), and then took a short train to Wengen. From there I hiked up to Maennlichen (this uphill hike was fairly strenuous, but everything afterwards is easy in comparison). From Maennlichen I continued on to Kleine Scheidegg, ate, and then went up to Eigergletscher. From there, I hiked west back down to Lauterbrunnen. This route took me all day, but it's definitely doable, and the views were incredible.
I left around 10.00 Saturday morning, took a train to Grendelwald then a lift up to First. From First, I hiked to Bachalpsee, and then to the top of Faulhorn. If I had arrived earlier, I would have definitely tried to go to Schynige Platte, but instead I just hiked back down to Bussalp and ate. From there I took a bus to Grindelwald and a train back to Lauterbrunnen. I got back to Lauterbrunnen perhaps a couple hours before sunset, and I hiked at a pretty leisurely pace.
I walked from Lauterbrunnen to Stechelberg, stopping at the Trummelbach falls along the way. The Trummelbach falls were neat, but maybe not worth the price (~10 euros I think). From there, I took a bus back to Lauterbrunnen and then trains back home.
My advice to anyone who only has a little bit of time to spend in the area is go to the top of Faulhorn, or even stay at the berghotel up there. I saw so many people going no further than Bachalpsee, but trust me, the view at Faulhorn is worth it.
Also, here's a helpful map of the main trails in the area with rough time estimates for how long they take. You can pick up a similar printed version at the information centers at any of the main train stations.
www.swissholidayco.com /Public/Assets/User/fi les/Map-of-Jungfrauregion1.jpg