Both GR2s and Excel-Gs are just stock replacements. They aren't designed to improve dampening.. that said, when deconstructed GR2s are better made than Excel-Gs, despite what KYB may tell you. (I think they may be trying to phase out the GR2).
I don't know the spring rates for STi springs off the top of my head, but the Eibach Pro Kit springs are progressive and have very soft springs rates. Which is good for ride comfort, but does little to improve handling. They are more for the looks of lowering while retaining stockish handling and ride characteristics.
I don't know about good struts AND springs for $700.. a set of struts that will handle upgraded springs well will probably cost around $700 alone. If you're really wanting to improve handling then I would look for D-Specs and RCE Black "regular guy" springs. Problem is, the D-Specs will run you about $800.