George,
It was Audi customer care themselves who told me about the extended guarantee, when I had thee packs go withing one month. And unusually they changed all three remaining old style pack for newer versions even though they had not failed (yet anyway).
I would go back and have a good old winge, ask to speak to a supervisor. My A2 was 5 years old 2 days ago, so I am not covered now, but as I had no problems in nearly 2 years I don't worry anymore, and like you the performance did improve a lot. But these parts are identical to VW, Seat and Skoda, so they will be covered, I'd ask why not Audi too? I'd quote this site as other members have successfully claimed coil packs outside of the normal warranty but within 5 years. You see my name, use it. Bradford Audi did the work and were informed by Audi about the extended warranty.
My idependant service provider told me about the price for coil packs falling to circa £12 each. I don't work on the car myself but I understand that it's not a difficult job. £150 is well OTT.