Keeping jars of paint from drying up

Eric, with most paints, the carrier, as you call it, or binder, usually doesn't separate from the pigments, (metallics, again, are the exception) but the solvents do. When the binder is no longer diluted by the solvents, it begins to polymerize. So the principle is sound: keeping a paint mixed does help to preserve it. Paints are formulated to be stable in a fully mixed state, although some consideration is given to storage.

The difficulties with your method are that if the cap or lid becomes loose, a real mess can result, even if there is no obvious leakage. Solvent can compromise the sealing material in the cap (unless it's a metal to metal seal), and once that's gone the paint is history. (Paint in liquid form, or in contact with its liquid form or the vapors thereof is a lousy sealant.) The other is that you have to clean the cap every time you open the paint.

I alternate by sitting the paint upright and every once in awhile turning all the bottles upside down, repeat...I believe this helps keep the carrier from separating from the pigs...

Ken, you get a gold star for applied intelligence! Well done!

Most modern paint has a nearly unlimited lifespan if protected from solvent loss and contamination. You are doing exactly the right things, with the possible exception of adjusting the viscosity (if you used a compatible solvent, then you did the right thing.)

Metallic paints are the exception. Metallic pigments often do degrade over time due to their peculiar nature. However, proper care will insure that they last as long as possible. Note that Alclad is a lacquer, and may have a longer, or shorter, life span than other metallics, depending on the metallic pigment. That said, I've never heard of the stuff going bad if properly kept. Don't try to adjust its viscosity, though. For that, you need to know the exact solvent composition of the Alclad, and I don't think they'll tell you.

Not only are you not wasting time, you're saving paint and $$$$.

I've adopted a method that seems to combat any unintended loosening of lids, and haven't had any paints dry out, or lids that were painted on since. I use Tamiya Acrylics exclusively, but this method should work regardless of brand.

I cut a square of Glad Press'n Seal plastic wrap, and place that sticky side down on the clean lip of the paint bottles and carefully screw on the cap tightly. Then I am very careful of keeping the bottle upright so that paint doesn't get onto the underside of the wrap. This prevents the lid from getting glued in place, the paint from drying out and I even manage to re-use the wrap.