I can help if you'd like. Did a lot of research recently. @sobanoodle is a Legacy guru also.
Externally you have a few main external visual differences. Pre-facelift and facelift, and then the optional S-Package (basically the SpecB of the BM/BR).
Pre-facelift standard:
Pre-facelift S-Package - Note the different fog surrounds, lower grill and black internals in the headlights:
Facelift - note the different grill (upper and lower) shapes, bumper shape, headlight design:
Facelift S-Package - basically the same differences as the Pre-facelift S-Package had but applied to the facelift:
The main features to look for are:
Media controls (left side of steering wheel)
Cruise control (right side of steering wheel)
Eyesight (Only an option on facelift)
Push button start / keyless entry
Interior (Cloth, Split Leather, Full Leather)
Headunit (Few options here, LCD, non-LCD, Macintosh) - Note: Even the basic audio packages are really nice (Harmon Kardon as standard).
5AT Auto vs 6spd Manual (for the 2.5GT)
Think that's most things covered...