Subaru engine vibration / shake

Hi all,
Have a question for anyone with some Subbie experience. Car is a 1998 Legacy Outback, 2.5L, Auto trans, 113K miles. Timing belt was SUPPOSEDLY replaced at 90k(I'm not sure). No maintenance history available. The engine has some light vibration (not enough to spill your coffee, but noticeable) when idling, and this vibration / shaking increases noticably with rpm especially in the 1500 to 2500 rpm range. The vibration is not readily apparent while driving, though with snow tires on all fours it's somewhat difficult to tell. The car is also quite difficult to start when very cold - it kind of chuggs to life after prolonged cranking. I have read other threads here and on other BB's with the following answers:

1) Camshaft timing off
2) Injector fouled / fuel management problem
3) Ignition, plugs, wires, coil...
4) Head gasket leak
5) Short skirted piston design
6) Broken/bad motor mount
7) Some subbies simply vibrate and some don't (yeah, BUT WHY?)

Any help appreciated. I'm thinking of starting with ignition components, and perhaps moving towards the injectors / fuel system and then timing belt(properly positioned?

Thanks,
foureyedbuzzard

if your car idles ruff instead of blaming your fuel injectors right away i would replace the fuel filter that would explain why your car idles ruff and when you accelerate from a stop ie 1200-1800 rpm range thats when you can "feel" your fuel system the most as apposed to when your giving it lots of gas i would also change the air filter just for the hell of it...i would replace that before i started playing with the fuel injectors

UPDATE:

Just did a tune up, plugs, wires, filters, etc. Found really dirty throttle body and nasty EGR valve. Good news is there doesn't seem to be any valve or head gasket problems. Vibration pretty much gone(relative thing with a Subbie), car running much better :)