Just got my missus a 1.6vetec focus last sunday and I like the handling,but not the guttless engine,I have only driven it once with her sitting next to me, so I couldn't give it the beans,I'll have to take it out by myself to see what all the fuss is about.
I think she should have waited for the 1.8 ,so go on fella upgrade you car.
Get it above 4000rpm, that's where the engine's happiest. If you try putting your foot down at low rpm, you'll be disappointed. Try keeping it a gear lower than you would normally use, ie 3rd at 30. The high gearing takes a little getting used to. Being able to do 60 in second isn't really normal for the engine class (IME).
Just an FYI, 2k rpm relates to 10x the gear used, 10 in first, 20 in second etc.
As for the OP, unless you want the toys (and a younger car), I wouldn't bother. The 1.8 is a fair bit heavier than the 1.6 (iron vs alloy block), and so takes the edge off of the extra 15hp. The fuel economy is likely to be a few less than you currently get, which is already quite low. You should be able to get 37mpg combined from the 1.6, so you might want to look at how you drive, not what you drive.