If it gets full iOS updates for two years then it's a non-issue. My concern would be that if the iPad 2 is discontinued next spring, when iOS 7 is announced next spring/summer that there are significant features missing from the iPad Mini due to the lack of horsepower, and then when iOS 8 is announced the following year the first gen iPad Mini isn't even on the list.
Again, I'm not saying this will happen. Apple, in my opinion, has a good history when it comes to iOS updates and might keep the iPad Mini on the list for three years or more. I'm just looking at the pattern for the original iPad, whose hardware was supported with iOS releases for two years, and extrapolating. Obviously that's an incredibly small sample, and not nearly enough to be confident in the pattern.