I haven't been there that time of year, so I'm not sure what hiking would be like. We were there last month and a couple of the trails we took seemed like they would still be easy to do at least until it got very snowy - like the panorama trail around Blumental, or even just the hike up from the train station in Grutschalp to Murren.
I did want to note that the Swiss Pass (and saver version) will get you all the way up to Murren, not just to Interlaken. We had a Swiss Saver, and the only things we had to pay for were - the cable car to Schilthorn, the cable car to Mannlichen, and the funicular to Allmendhubel. All were 50% off. There are a variety of passes, so I'm not sure exactly which you are getting, but if you get the actual Swiss Pass, it covers a lot, including buses, boats and streetcars.
If weather doesn't cooperate, I thought I'd mention a couple other places that we really liked that weren't Alps based - Murten, which Rick talks about in his book. Great views from the wall walk you can do, and just a lovely little town. There are hiking and biking options around the lake there that might work even if Alpine hikes are out; Fribourg, which was a lovely city with an amazing cathedral; and Vevey and Montreux - the walk from Chateau de Chillon to Montreux was beautiful. Both Montreux and Fribourg have funiculars up to some higher elevations, which we didn't do, but I bet the views were beautiful.
