DH and I both went and studied history (another "useless" subject???
), met over a seminar table there, and I look on the whole time as one of the best periods of my life, even though I've only just finished paying back the debt - over 10 years later (when I was teaching I didn't earn enough and kept deferring it!). DH has a PhD in medeival history and now has a fab job in IT, I have a PGCE, but went back to uni again and got a law degree, now a solicitor. Neither of us could have our jobs without our degrees.
I agree with Ellbell - I think a higher education level of learning is of value in its own right. DH is a case in point - his degree and PhD have nothing whatsoever to do with his degree, but he swears that having to learn medieval latin and reading manuscripts for the PhD meant he could learn any computer language. And it seems he was right.
However, if DSs don't want to go, then so be it.