Like other companies, Pentax gave different model names to their cameras based on where it was being sold. In Japan, the P30 was the same as the P3 in the US. The P3n is an updated version of the P3. So what I have is the Japanese-named update to my P3. Make sense? If not, ask Pentax what they were trying to do.
The difference the n designation makes is the additon of an aperture-priority mode to the exposure control options. That's it.
There's also a variant with a t designation (that would be the P3t or P30t, for those of you who care), and the sole difference is the split-image focusing aid in the viewfinder; the n version has the common horizontal split; the t version uses a diagonal split. Whether one is better than the other depends on personal preference.
Mine's another thrift shop find, bundled with two other cameras that I wanted. That's not a bad deal.