Hi Kevin - you have obviously had a good run from LPG in your cars.
Unfortunately, I don't share your experience with LPG - I have a 2007 Jeep Commander 5.7 Hemi with LPG. About a year ago I turned it off and have run on Petrol ever since. I think 25,000 miles is about the limit before the problems kick in such as top end wear, valve seats etc, whatever anyone says. And the performance, both horsepower and miles per gallon, is massively better on Petrol.
I have heard it's easier for older, carburetor, engines - I know it's certainly easier and cheaper to convert them - this may be the issue I have with the Hemi. Admittedly, to get a proper, high tech sequential injection Prinz or OMLV conversion with valve saver drip feed on a modern engine like the Jeep, it's ~£2500. The pay back is too long, before even factoring in all the other costs and down sides, and, that £2500 is up-front cash, of course.
The other problem is, I might be imagining it, but I'm pretty sure the available filling stations are contracting - certainly in the UK - possibly because there are less and less conversions being done - The number of big petrol engined 4x4's and cars that used to be classic candidates for conversion, has dramatically decreased - they have faded away over the last 10 years as the performance and economy available from big diesels has made them pointless for makers to offer. It's no longer possible to buy, for example, a new Jeep like mine anymore, only diesel versions - apart from limited production super-high-performance models like the Jeep SRT or Range Rover SVR, Merc AMG. I certainly come across plenty of "out of order" pumps at the filling stations. Before I stopped using it I was doing more and more diversions to get fuel.
Also, I hate the compromises on performance and, of course, packaging (ie. where the tank has to go?). I'm going to pull the installation from my Jeep so I can re-instate the spare wheel.
So, for me, I'm not a fan.