Well, if you get your machine guns shot out, you should be able to replace them when you re-arm. Since it's not putting on a new wing or engine, it would be nice to have. In the last FSO, I got jumped by a Zeke, and it shot out all but 4 of my guns, and I had only 3 shooting out of 1 wing. It would be nice though.
Remember it's not a new engine, wing, tail section, just a new gun or 2. Perk it