You tell a sorry tale. You paid a fortune for that Agila, which, with the Suzuki Splash, is a model I generally recommend to anyone seeking a small, upright car with good access, flat folding rear seats and a 4-speed torque converter autobox. £125pa tax and 42.2mpg are insignificant compared to the cost of swapping it for something else. It's now worth about £8,500. On top of which, the Nemo diesel Sensodrive is not a proper automatic. It is an automated manual, and these take some getting used to. (That said, the similar FIAT Qubo 1.3 Multijet Dualogic I tested drove very well.) You will benefit from £30 tax. But I don't think you will average such significantly better mpg to make the expensive swap worthwhile. The official combined mpg figure is 62.8mpg, but unless your motoring is mostly long distance open road you will not get anything like that. And the ride of a Nemo is van-like. Assuming you can get £1,500 off the Nemo, you are still looking at a gap of £3,000 to fund a replacement you might regret.