MP150 or MP200

I love PJ Harvey! Chak, I have been at this since 1965 and I have used most of those cartridges. Certainly the better ones as mentioned in reviews of the times. I have seen web sites where you can order replacement styli for antique cartridges. But, I am going to side with Uberwaltz on this one. Forgetting about MC cartridges there is no antique MM cartridge that can hold a candle to a Clearaudio Charisma in terms of build quality, tracking and sound quality. Some Japanese companies make fabulous cartridges, others just so so. Clearaudio makes consistently fine cartridges with build quality as good as any of the Jap companies as does Ortofon. Making generalizations is usually a mistake. 

You can buy modern replacement styli for vintage cartridges that use modern synthetic rubbers that will last for decades out side. Styli back from the day are probably bad by now. Not only that but quality control was pretty poor back then. I frequently had to go through two or three cartridges to find one with a straight cantilever and a stylus pointed in the right direction. But the bodies are just copper coils so there is no reason they could not last forever. But, today we have better materials and magnets plus we have CAD. The Goldfinger used CAD to position its 12 magnets correctly. I personally see no reason to visit the past. Modern cartridges are better if you can afford them and I can.

mcmvmx, You are right. Your arm is to light for the Nagaoka as it stand but, you can add mass to the tonearm. There are head shell weights and special screws of various masses. I always have to tune my arm a little to get it just right. I feel the same way you do. I would never by an old cartridge. I've used many of them back in the day and there is nothing special there. Modern cartridges are better in every way. Materials science has advanced dramatically since the 70s and 80s. 
The Ortofon 2M series has a much higher compliance. The Clearaudio MMs a little lower so you would have to add a little weight. Another cartridge that gets very little air play in the States in the Goldring 1012 GX
It is a high compliance, high output MM with a Gyger II stylus. Perfect for your arm. 

Chakster, whether the Sony or the Nagaoka cartridge would be better would depend on the tonearm. For medium to high mass arms the Nagaoka would be the better choice. If you had a really light arm then perhaps the Sony might be better. The Nagaoka has many fine reviews. I have not seen one on the Sony.

1+++ MP500:)  Very interesting system by the way. I like it!