you must be a fool to purchase a new car just because it gets 5-10mpg better or because it has $20 less tax per year....
Fuel costs/tax are a very very small part of all the expenses on a car..
It's only foolish if that's the only reason you're buying a new car. A lot of us like to buy new cars for the features and reliability (or at least to know that repair costs are covered by warranty). Choosing a vehicle with reduced fuel consumption does at least offset some of the inherent foolishness.
Since when has reliability and repair cost been an issue on a Jazz, even older ones ?
As for improved economy It all reminds me of government scheme to get householder to replace older central heating boilers with new condensing boilers. Sure the new boilers are a bit more efficient but they are expensive, complicated, unreliable and have a service life of about 6 to 7 years, compared to 40 years plus for an old style boiler.
Made much more sense to keep old reliable boiler and pay slightly more in fuel than to splurge out over 2 grand on a new boiler that will only give a short life, we have a top of the range vaillant condensing boiler, but it is a bit like 'triggers broom' in that it has had 3 new fans (yes condensing boilers have fans inside), a new heat exchanger a new pump (integral in boiler and expensive) and new control board, and vaillant are supposed to be the best you can buy. Our old cast iron 'dumb' boiler was about 40 years old when we got it and was still going strong when we fell for the stupid government scheme. The pay back period is key to the economics, you will rarely get back money spent for 'increased economy' unless you do truly mega annual mileage. Some people go for new tech, but for me infotainment screens in newer cars are a step in the wrong direction and I prefer tactile easy to set controls.