It's a largely pointless upgrade... fun for the feel of it, but just doesn't have the utility for an all-comers (or even most-comers) list.
Value can be found vs certain enemies or in certain missions.... but unless you know what/who you're playing and build a list specifically for it (which I don't care to do), then it's not much help.
I have, however, thought that it would be fun (in a campaign-style game) to have the Prey-that-Fights hunkered down in a nice big fortification (with turrets and everything) vs a Nid swarm that is fully Without Number (ie everything will come back on when it dies). Points skewed a bit.. for example 2000 pts (plus fortifications) of defender vs 1500 Tyranids.
Eventually the Nids *will* break through. The idea is simply to see how many turns the opponent can hold them off. Then in the next game, the better the defender did the more they get (say they had to hold off so that certain supplies could be evacuated.. if they last long enough, free power swords for everyone!). If the Nids swamp them quick, then the transports had to lift off extra-early (less wargear choices/special units for the guy next game).
Khira'lyth