Joe,
Any gasses getting past the pistons/rings under compression is indeed described as blowby. Of course it gets up into the valve cover. The area under the valve cover "comunicates" with the rest of the crankcase. If there is pressure down there, the pressure will also be in the valve cover. To determine the condition of the engine combustion containing area you must perform a test. A compression test on a warm engine will give us some basis for judgement. Take all the plugs out, block the throttle open, and disable the ignition system by removing one of the PRIMARY (small) wires from the coil. Now, insert the gauge probe in cylinder number one. Crank the engine over exactly seven "strokes" (you'll know). Record the result and move on to the other cylinders in turn. Next, get an oil can (the pump type) and just before doing each cylinder again, give that cylinder one full pump of oil. If the numbers jump significantly, you probably have an overhaul staring you down. I would prefer to see a cylinder leakage test, but most "civilians" are not equipped for this. However, it is much more definitive.
If your results show serious wear, the only thing other than an overhaul that you can do is add oil frequently or stop driving the car. Sorry.
Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon