If they're rusty, then yes, you'll want to replace them.

Not sure what model year you have but I flipped a Fuji Absolute a couple of years ago that had a 4130 frame with an integrated RD hanger. IMO these frames are of reasonable quality and worthy of upgrades. Replace the rusty cables and housings. You can get a cheap cable set at Wal-Mart for like $5-$10

Also........a drive side pic of said Fuji will help you get a lot more advice from the peanut gallery.