I had a LPG conversion on my old Alfa V6. I got the same warnings about valve seats but if you use a bit of petrol now and then it's ok. I did save a lot of money but it was a PITA too as the tank only allowed you to do 200 miles. I was always in the shell garage!
The 'old tank' did 250K miles, at least 200K on LPG, and was quite happy. Lost a little power though, but who cares when cruising on the motorway? Saved me a fortune, kept the engine clean and was kind(er) to the sparrows and squirrels