I am replacing my mids right now with catless. I was going back and forth whether to get headers and catless or just catless. The members here seem to think headers and catless are around 25whp gain (give or take 5hp). I also read just catless being good for about 20whp gain. So, headers didn't seem a good financial choice since I am going to keep the motor stock and hit it with a soft shot of nitrous. However, I have been told where headers come into play is when you start going bigger shots, SC, or turbo and need the extra breathing room. Any intake port/polish, new heads, cam upgrade, and the like will benefit from some nice long tube headers. Anyway, that's what I read.
If you want a nice handling upgrade you can call Stinker at JTSVP and get his Energy bushing complete kit. Changes all the rubber bushing to polyurethane bushings. I did it and can't tell you how well the 5000lb beast corners now. Good luck