I quickly read this thread and wanted to give my two cents. I would repot in the dead of winter or if needed early spring before much growth starts for best results. As long as the media is not completely frozen solid to the roots of the plant when removed from the pot just rinse somewhat softly with water (or you can let the soil attached to the roots remain and repot all of it into the new media. I've always used 1:1 or better in my opinion 2:1 Canadian Sphangnum peat moss : pool sand (found at a pool supply store) I've also used perlite in place of the sand but prefer sand for no good reason. Pool sand can be bought at pool supply stores. I like to stay away from watering with tap (mine is 99-105 TDS) constantly but used to when I ran out of rain water. I grew many plants for a long time on tap + 100 TDS that I consider hardwater but did flush with rain water. I mean I watered with rainwater intemittently. My opinion, if you have to use tap but try and use rain water in stages to reduce the hardness. I currently have three rain barrels and keep adding them as my collection grows because pitcher plants are sensitive to cations. Also try and beat 6 hours of direct sun in summer.
If the plants have been in the same pot for 2 years, yeah repot, and that may be the issue. I agree with several above good posts. If you have a stagnant plant after meeting all of the requirements which in my experience are not completely necessary, it happens. I've been sent a few plants that just never took off for me and others that took over. If all of the plants are acting the same maybe change your water source, sun exposure, etc. If one is acting stale, it happens. I would repot atleast every two years or make divisions in winter or spring. The NASC auction is every spring and is a great way to add to your Sarracenia (or other) collection.
Hope this helped. Good Growing!