FYI: The little lip in the pictures is not the original Spec-D rear end... the lip was a special order item as the Spec-D came with the WRX spoiler like I have on mine (and Ciaran WRX on his blob). Don't like the lip as much, the WRX spoiler is right for me.
Pro's:
Goodies at no extra cost like Fogs, Leather, SatNav - But still full STI performance with DCCD etc.
More comfy to live with on daily basis
More chance of one which had an easy life (typically more mature owner)
Bit more rare than just a normal STI
More discrete look (if it is your thing)
Con's:
Same EJ257 issues (2007 apparently stronger engine than '05-'06), so may need to uprate bits if looking for more power.
Higher tax for pre-'08 due to 2.5 vs 2.0
Bit thirstier for the same reason in standard form (once you tune economy is out the window anyway!)
More weight due to extra soundproofing and other toys etc
Less track oriented if that is what you are after (compared to JDM / Spec-C / S204)
More discrete look (if it is not your thing)
Horses for courses lads... though would say that by now - if buying a Hawk STI - it is more about condition and price, so even if you want the bigger spoiler etc, you might still get a better starting point in a Spec-D for the money you'd spend if going down the EJ257 STI route.