You say it smells, but so does petrol?! Petrol vapour is more flammable and dangerous than LPG, so the 'danger' issue is incorrect.
I got a factory-fitted LPG Astra so I can use it in the london congestion zone for free. The performance is the same as petrol, but £20 for a tank, not £40/50 like it would be for petrol.
The only downsides I see are finding someone to service it, but just like finding someone to fix my supra, once I've found someone competent then it's not an issue any more.
Also not all garages sell the stuff, but again once you know where they are, then problem solved. You can always run on petrol if you run out of LPG anyway.