Right, where do I start.
In terms of interior, whilst the Focus doesn't have the most exciting interior, it is a much nicer place to be than the Astra, it is higher quality, and simply more comfortable.
Half the dash is painted (badly) in the Astra, and this shows. It also wears quite easily - this was evident on my Grandmother's Astra after she had done just 14,000 miles in it, as well as the various plastic coatings that were peeling and rubbing off.
Then the drive - I drove a few and they all felt 'aged' at 5 years old, where as my 5 year old 1.6 Focus with higher mileage than the Astras I drove still feels as tight as my ST did the day I picked it up. I also felt that all the inputs on the Astra (steering, clutch, accelerator) feel numb and disconnected.
I notice the mention of sporty. A 5 door Astra doesn't look sporty either, but then the Focus does look a little sporty in three door guise. Also, if you're interested in something looking sporty, would you not rather something felt a bit sporty to drive? You do not get this from the Astra, but will get a sense of this from the Focus's excellent (in the context of family hatchbacks) chassis.
There was a thread a few weeks ago where someone was set on an Astra VXR, and he was discounting the Focus ST for similar reasons to you, and I believe he finally test drove one and ended up buying the Focus.
Quite simply, drive one - they are so much better!
On the Astra vs. Golf - there is simply no contest either, the Golf takes it every time.
FWIW, I also drove a 1.6 version of the latest Astra, and still managed to prefer the Focus.