Under EU rules, can I receive compensation if my flight was delayed by more than 3 hours but I didn't board it?

Vueling is currently experiencing problems at Barcelona airport, with many flights delayed by several hours. Assuming I'm at the airport and my flight is certainly delayed by more than 3 hours, can I simply book another flight and claim compensation later?

According to EU's passenger rights page:

In addition, if you are denied boarding, your flight is cancelled or arrives more than 3 hours late on arrival at the final destination stated on your ticket, you may be entitled to compensation of EUR 250 - 600, depending on the distance of the flight.

But it's not clear if I actually have to board the flight or if simply having a purchased ticket is sufficient. I presume it would be possible to negotiate with Vueling representatives at the airport, but I'd rather not wait in the inevitable 100-person line to their counter if I'm covered by EU law.