Even without a chip, an aftermarket DV is worth the money.
It acts to reduce turbo-lag. Note: don't confuse the performance gain of a DV as a gain in horse power - that's not what you're getting.
You're getting a reduction in the time between the moment you put your foot on the gas and the moment the turbo spools up to the point that it begins to produce noticeable boost.
I've got a Hyberboost DV valve by "Stratosphere" on a non-chipped 02. Results were immediate. No warranty issues, had the dealer install.<ul><li><a href="http://www.stratmosphere.com/hyperboost.htm">Hyperboost</a></li></ul>