I'm guilty in that I've yet to purchase for myself a Parker 51. I'm more into newer pens that can be serviced or replaced easily if it gets lost or damaged or something. That said, of the vintage pens I've had were some Esterbrooks ("meh"), some Parker 45s ("meh" in terms of writing quality, but the design and builds I like), and I think that's it. Wow. I got a PFM that I never got restored. I ordered another one which is due to be here this week hopefully.
But I have to ask, why do people prefer the aerometric P51 over the vacumatic one? Is there a disadvantage to one over the other or is it simply subjective? And if it's subjective, do you think there's a reason why you lean that way and not the other?
Oh, and I forgot, I have a few other "vintage" Sheaffers from the 1960s and I think one from the 1950s - nice writers, but nothing to write home about. They're not expensive. I got them from a vintage seller for cheap, and they all write just fine, but there's not enough for me to favor them over any other.