I've owned a P-16 and two P-18's (and a Hobie 14 Turbo and a Laser!)
Both the Hobie and the Prindle are very good boats. Some folks lean towards Hobie, some to other makes.
The H-16 tends to hobby-horse a bit more than the Prindle with a somewhat greater tendency towards pitchpoling. As stated above, the Prindle hulls have more volume so they don't dig in quite as quickly. I've always liked that benefit!
That said, you will learn the boat you are sailing. The PP factor by itself should not be the overriding concern.
As to parts, I've never had a problem finding anything I needed for the Prindle. Fortunately, I've never had to replace anything dramatic. Most of the rigging, sails, and hardware can be easily found. You might have more of an issue if you were trying to find a mast or hull.
The Prindle tramp is bound to the hull, while the Hobie is on a frame. Actual height is similiar, I imagine.
It will be tough to right either boat alone. Consider a bag, bar or Solo~Right.
If you plan on racing, Hobie likely has more class events.
The Prindle 16 is no longer in production, as far as I know but Performance Sailcraft is still building other Prindles.
See if you can test sail both then choose the one you like the best! If you can get a very good deal on one, then I would be comfortable saying "go for it".
Sheldon