Joacomau. Do it!!
It may sound funny, but the 17" alloys having 215/45/17 tyres, are SMALLER combination, than the 16" with the 205/55/16. Check it yourself
Your 17" will be 1% smaller, thus your car will accelerate 1% faster
About the consumption, nobody can tell for sure, since it depends on the rolling resistance of the tyre, so if you change tyre brand, there is no answer. Even if you fit same tyre brand, wider tyres mean a bit higher rolling resistance ( = higher consumtion) but on the other hand, you wheel will be smaller, thus accelerate easier ( = smaller consumtion). Go figure.. In any case the consumtion change will not be noticable imo.
With the 17" you will also have better handling and steering accuracy (not big difference though), and better looks of course. You will not have better grip, no matter what you hear about it, at least not because of the wider rubber. If you get better grip, this will be from better rubber quality, and thats all.
If you have factory suspension, you will not loose much comfort, by getting the 17". I changed from 15" to 17" recently and i was surprised to see that the comfort change is quite tiny.
The only bad thing is that you will have to be more carefull at potholes shaped like |__| not to hurt your alloys, but if you have factory suspension, you wont have to worry too much. Potholes shaped like \__/ wont be a problem.
Another minus, is that 17" tyres are more expensive thant the 16".