Pst? Firmfeel? Hotchkis? Worth it?

The Hotchkis stuff gets great reviews, as does the stuff from Firm Feel and Helwig. If you are not very mechanically inclined, a "Kit" may be a safe way to go.
I'm a bit more adventurous. Everything in my 70 Charger was bought individually. I have tried a few different parts to arrive at what I think is a well balanced car. Medium spring/torsion bar rates and large anti-sway bars give my car a decent ride with excellent handling on tap whan I need it. I'm sure that by buying stuff the way that I did I probably spent more, but in the end, the car handles the way that I like.