What do you get with the upgrade, do you get a full Fairfax 1 kit. I upgraded to X3 in a funny window, where the they were just about to release the AD2, so gave me the upgrade free. Many users seemed to get Fairfax1 full kit with their upgrade, whereas I just got a partial kit. I think because essentially I was getting the latest AD2 with my x3 upgrade. If you get the full fairfax1 kit, then I recon, go for it. If not then I'd wait for a better offer.
Keep an eyes on cclarry's posts in the deals section. He posted at the weekend an offer on the artists pack for around 99 dollors (pluginboutique.com), which was 2 kits, 2 kit pieces, 2 midi packs. After spending several tring to decide which 2 of each, I saw he had another post for the Fairfax 1 and 2 for 79 dollors (JRRshop.com) so I scraped plan A and went to this plan B. I beleive that with the Adpaks you then get your AD2 plugin update free anyway.
So as others say, there are always offers in the pipeline and last weekend 2 offers from 2 companies. January is around the corner, and post Christmas/New years sales with it, you could spend sometime figuring what kits you actually want.
Jazz brushes and Dry kit next for me I think. Fairfaxes are downloading as I type. JRR had me worried for a sec, took over 2 days to provide the reg codes, but I purchased on a non working day in a different timezone, with a company in a different timezone to the supplier.