"I can't/wasn't going to buy it anyway" and "But I don't pirate
everything" are classic pirate justifications.
Let's address the first one. Let's say that you have an Xbox 360, but Nintendo has just released a cool Wii game that you really want to play, even though you don't have a Wii. Now let's say that a clever hacker has found a way to make that game playable on your Xbox 360. Does that put you morally in the clear to steal that Wii game?
No? Okay, what if it were a GameCube game? Or an N64 game? Or a SNES game? At what point does the the theft of an old game become justifiable?
You can live without pirating old arcade games on your iPhone. As the now semi-classic Ihnatko essay points out,
you aren't entitled to anything, no matter how much you may want it.
Since you quote Ihnatko, who admits elsewhere he torrents movies sometimes with the intent of buying them when they become available, from the linked "classic" article:
"So long as you buy it as soon as its possible to do so, I can confidently reach for my "No Harm Done" rubber stamp. Some content is commercially unavailable because the publisher or distributor has no desire to ever release it. Ill even go so far as to say that downloading it illegally is a positive thing; youre helping to keep this creative work alive."
So in this context of old arcade "abandonware", where the publishers for a myriad of reasons don't make them available in any form, including many cases of them having gone out of business and the rights being unclear or copyright has passed to some company who isn't interested in publishing it, what IS the harm? Where is the crime? Who's being disadvantaged? Has anyone missed out on sales as a result? Clearly the answer is a resounding "no" where the game is no longer around. Is that an excuse? Possibly. A justification certainly. Can we live without those games? Of course we can. But given no-one is being deprived of anything, to quote Ihnatko, "No harm done".
And then there is the simple fact that there are a small selection of legal Roms available, like Gridlee. That alone justifies Mame's existence, irrespective of what use most people put it to. It helps to keep old classic games alive. That is the purpose of Mame: To preserve old arcade games for a time when the machines have all died as they will. Legally, if you own the cabinet, you are entitled to a backup, but realistically original cabinets are rare and expensive and generally not readily available to play anywhere, with a few exceptions. Pragmatically, people will get Roms any way they can to play as there are no other readily available way to play old arcade games. No reasonable person would argue that is immoral.
To play the Devil's Advocate, for any newer games being emulated and possibly still widely available, and I don't know if there are any, you could have a case the arcade is being disadvantaged. I do occasionally see pubs who has what appears to be Mame cabinets running a small selection of classic games. If they were in any way legit and available near you, then you could have a case for those games. But this is really stretching the argument.
As for the rest of your strained analogy with the Wii and Xbox: If you pay for the Wii game, and you could somehow plug it into a conversion unit which allows you to play it on the XBox, that is entirely justifiable, irrespective of what the actual terms say. If it involves ripping the game onto a hard drive and running an emulator on the XBox, that is not legal, but arguably justifiable if you actually paid for the game. If you then extend that to old N64 and SNES games, whose consoles are not available anymore, provided you own the games themselves, then that is certainly justifiable as it meet the no-disadvantage test. If you now assume people instead download games for old defunct consoles no longer sold new anywhere, but might be available 2nd-hand and whose cartridges or CDs might be found secondhand on ebay or elsewhere, you can argue moral ambiguity, as the game company, in this case Nintendo, is very much around and might possibly make the games available and sometimes do as a port to something like their handheld devices.
Whereas classic game enthusiasts certainly aren't entitled to any of this unless they physically own the game, in most cases it is justifiable irrespective of the label you choose to put on it, like Theft or Copying, since they are no longer available and most will never be. Moreover, there is a big difference between Legal and Moral. Whether it is legal to download a copyrighted work and whether it is moral are two separate questions. Let's not get into a debate about the efficacy of the Copyright Act, but in its present form with the Disney extensions it is not well respected and it is entirely possible for people to breach it wantonly and repeatedly without any moral scruples whatsoever and indeed be justified in doing so.