I put Prodrive Blue springs and KYB AGX struts on my car first...I thought it handled better in all situations.
Then about 20 months later I put sways, endlinks, ALK, front subframe brace, rear subframe lock bolts, tierods, and upgraded all bushings. The first thing I realized is I could now feel/notice the front springs/struts compressing in the corners (independently from the rest of the suspension pieces). Please excuse my lack of technical terms, but it felt like the tightened suspension was making my springs/struts work harder (but not overdoing it). So, I turned the setting on my front struts (AGX's are adjustable) so they were stiffer. This seemed to allow the strut/spring assemblies to better resist what felt like an increased load being placed on them.
When I only had upgraded springs/struts, there would still be times when the car's tendency would be to understeer (although less frequently than with stock springs/struts). However, after installing the rest of the suspension pieces, that is no longer the case (personally I think the ALK is a big contributor to the handling capability of my car). The only thing holding me back from pushing the car to the absolute edge of its potential is that I need a seat/seatbelt combo that will actually keep me in my seat...
Is it perfect? Well, I guess the concept of 'perfection' is always open for debate. But it feels as if the front spring/strut assemblies are complimenting the rest of the suspension pieces better now.
For what it's worth, I'm fairly certain that Prodrive Blue springs are not as stiff as your RCE yellows...and I agree with what mosc has said: Now I am more confident as to what is happening underneath my car's unibody because I can am getting (re: feeling) feedback that is more accurate and precise than before.
I suppose when I only had springs/struts I also thought I didn't 'need' sways and endlinks (for street driving mind you). But now that I have experienced the feedback that they give, I can't imagine not having them.
70 to 100 faster than you can say "whoooossshh!"