I'm 41. My SVTF gets 20-22 mpg around town, as high as 30 mpg pure highway (and I don't drive slowly... ever).
I'd say driving the only SVT Focus in the country is a big plus. I drove a (US Ford) Contour when I lived in Germany and I actually got looks from Mondeo drivers (and others).
But since I'm in the geezer crowd, I'd have to say don't spend 50% of you savings on ANY new car. Or 30% either. All it takes is one good f*** up and... poof it's gone. There's got to be a decent used turbo-diesel Golf you can move up to, no?