I have been driving Platz (2003) for the past two years. It is quite economical with fuel, has a smooth drive and starts with a single turn of the key. Automatic transmission, power windows, power side mirrors, digital odometer, adjustable steering, power steering with wide angle cutting, central locking. Its a bang for the buck. As far as its spare parts are concerned, let me tell you that except for the headlights, brake lights and bumpers each and every inch of it is identical to Vitz (1999-2003) and so all mechanical and interior parts of Vitz are 100% working with Platz, even the doors are identical. You don't break headlights and brake lights every month so that should not be an issue and even if it is, they still are available in the market. The addition of trunk is another plus point (when compared to its cousin Vitz).
About Liana I cannot comment because I have never driven it nor have my friends kept one.