I have upped the boost on my Skoda(!) and would like an opinion as to whether I should change the dump valve from std to something a bit more robust (but still re-circ rather than vent to atmosphere). Any thoughts?

Could be worth it if you've upped the boost -- there's been a lot of OE Bosch dump valve failures on the TT forums on both 180 and 225 bhp models, and apparently it's now an official Audi warranty job. Upping the boost will put more strain on an already suspect component.

They all seem to favour the Bailey type valve -- check audi-tt.co.uk or audizone.com for more details.