What viewers see on their computer is one of the most frustrating things about the whole Internet image sharing deal.
Firstly LCD monitors are crap! But we have to live with them because that's what manufacturers are producing and the public have been conned into thinking they are good (just like Plasma screens). Don't get me wrong I own a High Definition LCD TV 1920x1080 resolution. But the picture is well, LCD!
For computers I use CRT flat panels because images look beautiful and don't look like a mass of dots or have a watery look that Plasma gas gives.
You must set your Gamma up to meet the correct standard which is 2.2 on a PC and 2.0 on a Mac. As for colour variations on different computers - well it's up to the viewer to set their screen up properly (and that isn't going to happen!) Turning the brightness up to 100% on your LCD is false hope. More like 80-85% is more realistic and your photographs should look right on your screen at that settings.
Mate, there is not easy answer. But even allowing that your images look dark on a correctly calibrated CRT screen I can tell you that your images vary in darkness and contrast from one panorama scene to the next.
After just taking another look at your first tour the exposure looks pretty right but you have a lot of dark shadow areas and this has to do with the time of the day. The "Living Room" panorama shot is dark - too dark. Exterior shots look about right but again very dark in the shadows. This can pretty easily be improved with RAW editing and some special tips I can teach you.
Bedroom 3 is very dark. Even looking at your thumbnails show the colour variations between scenes.
..... and you are right! it will boil down to how much time you want to put into real estate tours as far as time is concerned.