I just replace some hose and all metal cooling tube (rusted to the bone),
the only truly damage hoses were the 2 heater cooling line that goes from
the back to the front, parallel to the 2 big cooling radiator tube that
goes to the front radiator. The interior of those one was quite ok but the
exterior was getting very bad (crack due to rock and other stuff)

All hose where remove and inspect, you can see the one I change as a
precaution on my site at:
http://pages.infinit.net/engine/cooling_system_hoses.htm

To your question:
Original VW hoses have the part # printed on it, they are of extremely good
quality and should last over 175/200k miles. To test the hose compress one
and feel if they are still firm, on the contrary of popular belief, an old
hose will be VERY soft and you should be able to feel or see some "Crack"
when compress. The hotter one should be change first. (Check my site for
this information.)

A hose will generally break around her attach point (at each end) or start
leaking around those point. But sometime they just blow!!!!!!!!!!!!!! (very
rarely)

Regards, Ben
http://www3.sympatico.ca/huotx/engine1.htm