For locals with a transportation pass it's free.It is also a lot cheaper.
There aren't that many hotels in Bryggen. This being said, absolutely, Bryggen and Sandviken need light rail extended there.For locals with a transportation pass it's free.
I've taken it a couple times recently to and from the airport. There has been lots of room from the airport to Lagunen, but very full from there into the city.
Some tourists on a budget will take it to save money, but having lots of luggage will be a hassle when busy. Also, Bybanen doesn't serve tourist staying at the hotels around Bryggen.
Bergen light-rail construction design was orientated at german BOStrab, saying you don´t need signalling in short tunnels. Putting a station into the tunnel changes something in that matter, because Bergen planners until now avoided that. That´s quite interesting to see, how they will do it. Poznan and Cracow do have those tunnel-sections with stations, too. Tunnel light ist always on and in Poznan both tracks are seperated by a wall. The tunnel is equipped with SIL2-level tram-signals like traffic-lights. Basically this works well for trams.^^ Here is a better picture of the route chosen. The underground station will be placed at the spot marked "NLA".