It would be the cost of it that determines if you go ahead.
If I got a brand new car and I was going to keep it for 5 Years and do about 50-100k miles, then yes I'd do it.
But with the Zed, to make you money back in savings from the LPG installation, it is going to take a lot of miles....
I.e. imagine the installation costs £10k - and You save 50p and Litre and save an extra 10p per mile. - You'd need to fill up 14k litres of fuel to break even. (This maths is a total crap comparison, but just to give you an idea )
More Maths - With those numbers above - at 30mpg - You'd need to do 90k Miles