Boosty, I can't remember how far that little piston is supposed to stick out.
Maybe Bob can? But, seems to me that buying a new spring would be the best way to tell. If the length and strength of the new spring are the same as the old one, then look elsewhere. Also check the piston and bore for scratches or scuffs or evidence that the piston was stuck in the bore. Otherwise, what has been said seems correct to me. That is, the higher the engine temperature, the lower the oil pressure. The slower the engine speed, the lower the oil pressure. But with 200K+ mileage, as the others have said, worn bearings are the likely cause.
Oil pressure is very sensitive to engine temperature. Some oils really thin down when hot. Was the car running hotter than it used to? Here are some things you can try in addition to the new spring. Try heavier oils: 15W-40 or even 20W-50 at your mileage. Run a 180 thermostat. Install a transmission cooler. It is not an obvious benefit, but in addition to making your transmissions live longer, a separate transmission cooler will drop your engine operating temperature (and increase your oil pressure) noticeably.
And, since the engine is out anyway, if you have the time, put it on a stand, pull the pan and plastigage the main and rod bearings. Better to find a bearing problem now than after it is back in the car.