Well, personally, I'm not sure a Mustang is really any less versatile than a P. One pickup, similar position, one tone control.. maybe a Precision has a bit more range, but in a full band mix? I think either will be fine, and will ultimately just sound like what it is. Even if the Precision pickup is more versatile, it's not like you'll get Jazz or Ray tones.
Really, the most important thing here is the scale length. Maybe the P is better value, but if you really do prefer the playability of a 30" scale, that's $2k poorly spent - much less value for you than spending it on a 34" scale you don't like as much! I think this is where you need to narrow it down.
The Mustang might be twice as much as a JMJ, but you're paying a premium for a US made instrument; and frankly, if you can't get a lefty JMJ, it isn't even a comparison. I've only just looked up the Nash, but it appears it has a belly cut and maybe an arm contour too - quality of life improvements that are worth a good chunk of change. For what it's worth, I had a quote in the UK to strip my Mustang, add the contours, & repaint.. better part of £1,000. So if you'd like those ergonomics, I'd pay a small premium for them alone.
Really, the most important thing here is the scale length. Maybe the P is better value, but if you really do prefer the playability of a 30" scale, that's $2k poorly spent - much less value for you than spending it on a 34" scale you don't like as much! I think this is where you need to narrow it down.
The Mustang might be twice as much as a JMJ, but you're paying a premium for a US made instrument; and frankly, if you can't get a lefty JMJ, it isn't even a comparison. I've only just looked up the Nash, but it appears it has a belly cut and maybe an arm contour too - quality of life improvements that are worth a good chunk of change. For what it's worth, I had a quote in the UK to strip my Mustang, add the contours, & repaint.. better part of £1,000. So if you'd like those ergonomics, I'd pay a small premium for them alone.
it’s been an awesome spring and summer with this bass! 
