The key point here is my opinion is based upon verifiable facts written into copyright-law itself. Nintendo themselves even reference the legal right the make a backup copy in their own ridiculously stupid anti-piracy web page. re: downloading ROMS for a game you own. I am no less qualified to state what I have so far, than any actual lawyer is, because a certain amount of speculation is involved. Even a lawyer cannot say for sure without a hardcore established case-history of lawsuits to reference one way or the other. My assertions are far more reasonable in any case, and just as sound as a lawyer who would say "well, based on current law there is nothing that says this activity is explicitly illegal/legal".
But back on topic. It is pretty safe to assume Emulators are legal based on existing lawsuit results, and the lack of lawsuits against popular emulators in general. It is important to note that Emulation is not a new concept by any means, just that game console emulation is a relatively newer branch of the field.
Sony never actually won against Bleem! for instance, when they took the company to court, although Bleem! went out of business soon after saying that the lawsuits had damaged their finances irreparably. The only Emulators I would stay away from are those that absolutely require a BIOS to run games, and actually provide that BIOS file with the emulator.
In general it is assumed BIOS ROMS/files/whatever you want to call them, will be obtained by the user just like a game ROM would; from the users own console, using generic / non-illicit dumping hardware.