While the question is now closed (and not migrated, thankfully), and random's answer addresses the "Don't migrate crap" rule, I want to point out a few issues with the assumptions you lay out in your question:
Firstly, the default option for an off-topic question is always, always close it as off-topic. You don't have to find a more appropriate site for it: most of the time, there is no appropriate site for it. When you start off with the default position of "this question must be migrated since it's off-topic", you start bending the rules of what's really acceptable on the other sites. "Well, Super User looks like the closest fit, so migrate it to there because it's off-topic here."
Your second point, that one ought to migrate a question if it'd be welcome on the destination site, is far more on-point. Super User looks like the closest fit, but is it really on-topic there? Would they welcome this question into their corpus? What's the value-add for them to have this question?
And secondly, "it's too old" is an adequate reason to not migrate a question, particularly a question like this.
A low-quality question that's two years old with no activity in the meantime is a question that's functionally abandoned by both the original asker and the community. Nobody is going to use that question's migration to learn about Super User or what's acceptable there.
Additionally, migration stubs are automatically deleted after a month. So you're only providing a method of discovery for people who see a long-dead question for the next 30 days. After that, it's as good as deleted on Stack Overflow and Super User (or whatever the destination site happens to be) gets a question that'll probably wind up only helping the flag weight of the person flagging the question on Stack Overflow.
Joel Spolsky once remarked on OnStartups:
One more thing I would add--this site has an unusual number of really old questions that never got an answer. If a question has been languishing for 6 months without a single answer, I'd say just delete it mercilessly. If it's important, someone will ask again....
While there technically is an answer, a two-word link to another site is not really the type of answer one thinks of on Stack Exchange.
So if the question was so important to the greater internet community that it must be preserved, it would've been re-asked sometime in the last 2 years, or perhaps more importantly, it would've garnered far more attention.
But in general, if you personally think a long-abandoned, off-topic question needs an answer, there's nothing stopping you from asking it again on the more appropriate site in a far more constructive manner and with the details specific to your situation.