Like I said, I don't consider composing and orchestrating to necessarily be the same thing, although they definitely overlap somewhat. I can compose a melody in my head, right? Let's say I did, but if I wanted a horn to play it, and it goes over a transposed high B or C (which is the limit of comfortable range for most). In this case, then I KNOW I'll have to transpose it down, or give it to another instrument, which is basic orchestration, yes, but maybe you'll see what I mean separating the two concepts.
All in all, I think composing refers to the building of ideas and structure, while orchestration is the execution of those properties.
I should be saying "no" because I barely play anything. However, as a kid I messed around with a guitar long enough to get a hold of all major and minor chords, as well as their relationships (thus allowing me to transpose any tune to any tonality at will). That, in turn, made me conscious of having perfect pitch, since my relatives and friends often asked me to listen to any given piece and immediately tell them the chords needed to play it along - which led to the real discovery of my own ability to craft tunes and work on musical relationships. So, there's always an added benefit when you know how a thing works - but only to some extent. For instance, I have greatly improved my piano writing in the last few years - without ever being able to play it. Same can be said of orchestral writing (my biggest strenght, I think), since nobody actually "plays" an orchestra, and I have never been a conductor.