Having thought a little more on it, I think the value of a Nimrod as a strike asset is in cases where nothing else can reach. We can't expect to have a carrier or a friendly airbase within Typhoon, F-35 (or until they retire) Tornado range, or an SSN within cruise missile range, of every possible target, all the time....
As for the value of carrying such a missile internally on a Nimrod... That I am unsure of. Given the value of a Nimrod as an ISR platform and what features are needed to make the best use of it (namely high loiter/persistance time) mounting weapons on it becomes less important IMV. Far better to have the Nimrod vector strike assets than to be used as a strike asset itself. ...
-Cheers
In this case, I'd say missile range is crucial, & while I think NSM could be useful in general, I'd rather our handful of Nimrod MRA4 kept further away from nasty people than the range of an NSM, if possible. Storm Shadow, or even better, an extended-range version, would be preferable.
There we have it: not a routine thing, but an occasional use for high value (I take it for granted we wouldn't waste such rare & expensive aircraft on low-value targets), time-critical (can't wait for an SSN or carrier to get there, or they'll be busy elsewhere until too late) targets. Not cases where there'd be any point skimping on the missile.