Hello!
I'm from Brazil and also thought about that, so let's see:
If I search about café or cafe (it means coffee in portuguese), the Google Adwords broad match doesn't care much, it gets them as the same, with Local Search Volume of 3,500,000 for both.
But in the Google Adwords Exact Match, it goes different:
Local Search Global Search
café 27,100 60,500
cafe 18,100 246,000
So, it seem that you can use in theory both keyword for Broadsearch, but you are going to lose some when it goes Exact.
So you have to see which one is the best one for you, that brings more traffic and at the same time a good conversion.
1)You're going to have a keyword ranking for each of the words.
2)I don't recommend you to hide a "no accent keyword" because Google can see it as a Black Hat and punish you.
3)And if some of the words don't make sense without the accent, you should use them with it, because you can't forget your users, because won't make sense to them either. Therefore, it's going to have a big bounce rate.
Hope it helps! =]