If you want to change just for the sake of it, then go for it: They're great cars. However, if it's a cost-saving exercise then you might be better off sticking with the Zed.
By the time you've inevitably spent more on buying the BMW via the higher sticker price and losing on whatever the Zed goes for, you then need to add in the extra cost of diesel itself, plus the BMW-tax for consumables, and extra cash for the modding. By that time, and over the course of a few years, you may actually not be any better off financially.
It's just something to consider.