As pretty as Wengen is, we felt we saw the entire place twice in 90 minutes. I would be bored out of my mind 2 days there. If you love that scenery, then hit up Gimmelwald, Grimmelwald, Murren, etc. It's all in the same area. I would just stay in Interlaken and pay half the price for a hotel and get better restaurants then visit those other places - and take a boat to Thun and back.
Paris is a multi-level city. You can hit the normal tourist spots, but you can drill down into various districts and find many unique attractions. You can definitely keep yourself occupied but it takes some research and effort.
Colmar is a great choice but again a day or two is enough - unless you want to rent a car and go to all the Plus Belle Villages within a few miles or up to the Konigsberg Castle about 10 miles away.
I felt Bruges was a bit over-rated. I made day trips to Ghent, Oosterand, etc. Bruges has some water and nice little city center like a mini-Brussels. You can see it all in an hour or two.