I have to admit, I don't see a whole lot of gain after about five years. As everyone is saying, CS knowledge is timeless, but aside from the basics, it's really not that useful outside of research positions. Most of software development is making CRUD apps, integrating APIs, and other tedious but non-complex stuff like that.
Regarding prestige, most of the time when I'm at a non-techie party, when asked what I do, people have nooo idea what "software engineer" means. :-)
Isn't that sort of like saying that most of the restaurant business is flipping burgers? Just because something is more common, that doesn't mean you won't be able to move up the food chain a little after 40 years of programming. Companies still have plenty of hard problems to solve in network performance, hard drive performance, UI architecture, cryptography....
You don't really "work your way up" from years and years of CRUD apps and API gluing to hard CS. In fact, if you get a CS degree and don't go straight into hard CS, you will forget most everything you learned in a few years, not to mention miss out on years of focused practice.
That or you can write code in whatever spare time you might have from your 8-10 hours a day job. Based on what's said around HN, people putting in 14 hours a day coding are not that uncommon these days, so perhaps it's something programmers are better get used to. Remember to blog, have a rich github portfolio, contribute to OSS and run your own consulting consulting company in the spare time from your full-time job.
"So what advantage does a 60-year-old .NET programmer have over a 27-year-old .NET programmer when they both have, at most, 5 years of experience doing .NET programming? Absolutely none."
Umm, I would say that 40 years of experience building software applications is a pretty huge advantage. I've been writing iPhone apps longer than most of the older guys I work with, but that doesn't mean that I know more about development than they do.
Languages and technologies may be temporary knowledge capital, but they're also one of the least valuable things a good developer will have.
As far as prestige and foreignization? It's amazing how much things can change in 5 years. Programming is (sorta) becoming cool thanks to things like The Social Network. 2/3 major operating systems are developer almost exclusively in the United States. All major programming languages are in English. Software development isn't going anywhere in the US.