I am using X55 as well. It will be dimmer after wearing the Glasses. You may try to adjust different 3D modes via the remote. There are some mode which is brighter. The best way is using the Tuning disc to calibrate the settings of the projector to suit your taste.
It is of course best to use high gain screen to watch 3D and a natural gain screen to watch 2D. However, it all depends on your watching enviroment.