In todays age you have tor really think what makes a classic..
The Classic has a reputation nearly as despised as the P38 and I've said it many time over from experience that you either spend hours/days/years welding up a classic or you can spend time with a multimeter and a soldering iron with the P38, and having spent hours on my back under a Classic with sparks and metal splatter running down my shirt, I can tell you which I'd rather own..
Hence why I sold my 91 3.9 manual and kept my P38..
The values of the P38 are going up unless you're looking solely on Ebay where most spares/repair motors linger, even now you can snap up a classic for less than 8k as they tend to pop up on ebay occasionally.
Jeep XJ's have sky rocketed in value in recent times, no idea why my Dad had one in "murple" and he snagged it for £600 and gave it away a few years later, not very practical and incredibly thirsty for the size of the thing, IIRC it did 15mpg almost all the time..
As for LPG I run mine primarily on Petrol for that exact reason LPG has nearly disappeared from where I live and to be fair I factored in the cost of fuel when I bought it and to be fair to it with everything in tip top condition it is currently averaging 22mpg on my route to work which ain't bad considering my RRC with LPG did 12MPG on Gas which equated to around 23mpg cost wise, so any saving is was barely noticeable..
Would I spend 6+k for a P38? Hell no my Dad says the same about the 2dr classics he had one in the 90s he payed 1k for it he says to him they're still not worth much more than the £600 you could pick them up for a few years ago the £40,000 plus they fetch is hilarious
I payed less than £900 for my P38 4yrs ago, you can't find a running/driving one for that now..