Did you look at the old sock and filter to see if there was gunk/crud in them?
The ONLY thing I can think of is that you knocked crud loose and has now clogged the injectors... BUT... I can't see it messing with all the injectors... just 1 or 2... maybe 3.
Are you savy on fuel injectors ? If so, pull them and clean them up... even take them to a place that will bench and flow test them for you.
Worse case scenario, you spent a cuple hours and $50 getting them cleaned.
Trace your steps... When you changed your plugs, did you happen to mess with the fuel rail. Reinstall the old plugs for giggles...
2002 WRX Sold
2007 WRX Sold
2007 STi totaled
2007 Foz XT sold