Ive had the honour (hmmm) to sit on the selection board for some Navy chaps (and chappess's) and can honestly say that secondary duties didn't get a look in. We wouldn't be bothered if you spent your spare time dishing out meals on wheels. What we were looking for was "potential" in the next higher rank.
You could have had a shed load of secondary duties and been president of the local freemasons BUT if we thought you would have been crap in the next higher rate you wouldnt have got a look in.