Wealth / Knowledge – Perpetual??

My sister for all the uselessness and failure she has built her life into is way too sharp and witty.
She is someone in front of whom you feel that you are absolutely uncreative and what one'd say – can't think differently at all kind of person.

Was reading Pamuk's snow and had a bookmark with a Socrates quote saying
"Prefer knowledge to wealth, for the one is transitory, the other perpetual"

Now its a good one and I never thought much about it and if I had thought too I would choose both or say its a tough choice and many many arguments .
But here's how I was cross questioned.

Tell me where does he say which one is perpetual. The line is open – he says one is perpetaul but which one.
I say its obvious – knowledge is perpetual.
She says how can you say that.
What was recognized as knowledge 100 years ago is not always relevant and you also forget things you learn.But look at wealth say a 100 rupee note/gold it is still the same.
So whats perpetual hmm.

Now only Socrates can answer that. I just cant.
P.S:
I related this to few friends and laughed at it and while some just laughed – one very well meaning and concerned friend lectured – you should have told her and educated her that you too must update urself and move on and make something out of your life and get a job. Some people for all their well meaning just dont get it neither the humor nor the facts – that you just cant change people.Somethings must come from within.
She followed it up with more concerned feedback about how I was not making an effort to settle down.
For all the pain they cause me I love enemies than the well meaning people I've been blessed with most of the time.
The last month has been as it is nasty at the office.
I've become/developed myself a outcast for most of my Office people.
If it wasn't recession and I being in a secure but terrible place where of all the sad things can possibly happen professionally – the chance of firings is the least – I would have updated my resume .
Saddest part was someone I hoped was a trifle better too seemed to be untrustworthy at times.That kinda upset me more than anything else.
It feels like being back to where I started from. Of course I am no longer the same but the place seems familiar.