In terms of representation, you're making the incorrect argument. Cerainly chinese dialects, hindi, arabic and farsi all probably have a far larger "user base" than Spanish. However, your argument purposely ignores the obvious fact that none of those languages are represented to the extent that Spanish is within the United States.
I don't see the problem with accomodating such a portion of our populace; how many presidential debates were available in English? With that in mind, I don't see the problem of having one in Spanish (and I don't imagine that all the candidates were speaking in Spanish, so what would be so difficult about that? There's no inconvenience there.
Regarding spanish ballots, you're mistaking linguistic ability and cognitive ability; it's not as if Spanish speaking people within the United States aren't aware of political issues, or they are inherently stupid. That's just an empty argument.
Regarding fragmentation and unity, citing Quebec is interesting, because you're making the argument that *language* becomes the root cause of such fragmentation. The situation there is far deeper than merely language, and in the end, language becomes a salient manifestation of the divide; it is the result, and not the cause, of other factors that created fragmentation. Correlation is not the same thing as causation, I always say.
I'd be curious to find the specific kinds of examples of your mother's shopping inconveniences. Market rules, if we believe them, would dictate that it is the shopowner's responsibility to ensure openness to a wide variety of customers; the failure to do so would surely lead, theoretically anyway, to an end to that business.
Locally, a bar was recently cited because it had a sign in the front window that declared "for service, please speak English." At a minimum, the bar has to take the sign down; at most, they will receive a fine for discrimination (that had not yet been decided). I imagine that you feel empathy for those people in the community who sided with the bar, and support its willingness to not serve a sector of the community.