wondering whether its worth adding a short section of flexible braided exhaust to my system ?

The main reason is to alleviate strain on the headers, and reduce the chance of them cracking

I have aftermarket Flowmaster headers and a 2-1/2" pipes

I would get my exhaust specialist to weld it in for me, he said not needed, but I forgot to mention to him header cracking is an XJ specialty

the PO did some poor welding on the pipe, which burned a hole and cracked it, I mig welded it up, but the crack has re-opened.
my exhaust guy is a wizard with Mig, I hate welding on non-shiny steel, while upside down, instead of on a hoist

 

I think it's a good idea.

 

I am planning something similar when I redo my exhaust with a new downpipe and put in a header. Fortunately my factory manifold is still holding up.

Would stainless steel make sense for the downpipe?

 

No stainless isn't worth it unless you pay for the good stuff.

I think a few stress relievers in the system would be a good idea.. the factory HO header has two in just the header.

 

I did this a while back. Unfortunately I had installed a flex piece made of 304ss and I am in CT. The mix of road salt, heat and exposure to abrasives ate it away in 3 years. Headers remained intact though...