I see Golf GTIs every single day, not rare at all. My neighbour has one admittedly, but I see at least one other every day. Not Focus ST common, but still common as muck
There's no reason an Escort Cosworth wouldn't work every day, after all, despite a lot of people forgetting that, they were built as a normal car, not some special mad thing that you can't drive.
However, technology has moved on a lot, so I think something more modern would probably be nicer to motor about in on a daily basis. But, there's no reason why a good condition Cossie wouldn't be a reliable enough car if looked after. Not sure I'd be too happy leaving it parked about though, could see it getting damaged/vandalised/stolen.
I think I'd buy myself a decent condition MK3 Mondeo or something for running about in, the have a Cossie as a weekend toy. Golf is ok, but not that special in my eyes. I'd rather have something cheaper to run on a day to day basis, then have something nice I could drive when I felt like it.