Jul 8, 2014 - 10:16 AM
Well, a visit to the Jungfraujoch is indeed amazing, see here for what to expect. It's perfect for that day, but only if the sky is clear so that you can be sure of getting the good views. Just take things slow and don't do anything else that day, apart from enjoying an ice cream (Mövenpick!) in Wengen or Kleine Scheidegg, for example. If the weather does not allow for the trip, then save it for another occasion and do a boat trip on Lake Thun/Lake Brienz, or something else in the valley. Or visit Bern if you like exploring beautiful cities.
Note that Interlaken itself is not particularly pretty. It's a perfect place for a rest day, but don't expect to see the best of the Alps if you stay in town. I would only stay in town if I was exhausted from the ride and wanted a full day of rest to prepare for the next drive.
I hope this helps with your planning!