The nominal gamma setting of .45 is designed to accurately reproduce the grey scale on CRT monitors. Some other contemporary monitors also are calibrated for similar gamma.
Setting the gamma at .75 is effectively "crushing" the gamma, that is lowering the middle grey. This effect is often referred to as "crushing" the gamma. With Panasonic cameras and their Film Rec Menu when Dynamic range control is invoked the blacks and gamma do seem to raise and the picture begins to look low contrast, washed out and desaturated. By crushing the gamma you restore the contrast and increase the color saturation.
These are controls you might do in color correction (if that is included in your post workflow) or can be done to the origional (as you have described) to create a more pleasing WUSIWUG look.
You do have to be careful however not to crush the gamma too much for display on conventional monitors. If you're looking at an uncorrected LCD display which has false brightness, what looks good at .75 gamma will come out dark on other displays. I suggest going no further than .55 or .60 gamma for this reason, unless of course you're going for a specific effect.
If you are using aggressive dynamic range setting (like 500%) then set your Panasonic monitor for "Film Gamma", then you can more accurately see what the change in gamma really looks like (assuming you import to post with Film Gamma Correction set to "on" on your 1400 deck) otherwise the monitor is creating false brightness that will also complicate setting a proper iris (unless you use the waveform function for that) because it is an LCD.
I would use great care with the film gamma settings on the monitor. The settings are designed to match film-out gamma curves, not REC709 monitors. You may end up with underexposed or noisy footage as a result. I would test.
Yes, I tend to use .55 gamma setting, unless I need more dynamic range. In high contrast situations, I will open up the gamma to .35... it's amazing how much info the varicam can record when you do this.