My opinion-
I would never have an item that was 100% repro - however I can see that if something is way over budget or simply unobtainable that there is a market for such things. Personally I really dont see the point in pretending that something is something else - a reproduction item will never be what it 'pretends' to be and never will be - repro is repro - end of....
....however; I believe that it you have an item within a collection that lacks a part, which is not readily available to complete, then I think it is acceptable to add a 'replica' piece, in lieu of getting an original. Now whether that additional piece should be aged to look like original is another question?
heres my issue; what happens when these things get passed on intentially or not. We all know that some people have so little regard for history that they intentially try to decieve by passing on replica or fake items as original - hopefully as collectors with suitable knowledge we avoid such items (though as in a recent thread on Mills bombs, posted by Millsbomber, these are getting to be a very high standard!!).
Now there is another situation; a collector adds a replica piece to an original item, unforseen circumstances means the collection is passed on - the aged replica bit is not acknowledged, and now forms part of what is classed as an original item. Now we have a situation where an item has been added with good intention, but which now forms part of someone elses collection as an original bit. In future years this 'repro bit' also may become recognised as a 'slight variation' or 'another type' to look out for.
I have a battle with my own concience about what is right or wrong in this respect....I dont think by adding a replica part you are doing any harm within your own collection - BUT in doing so are we unintentially doing an injustice to what, in all intense and purpose, we are trying to preserve????
(I myself have had some screws made for the SD2's to attatch the arming rod to the fuzes - as these are impossible to locate on their own. I have also purchased some M83 arming wires - in lieu of getting originals - as again finding any at present on their own has proved fruitless. HOWEVER, I have not finished these off to the standard of original pieces and made all attempts to catalogue them as Repro so as to prevent them being passed on as such.....they are not of a standard to fool anyone - just good enough as representatives!!)
.........hope this helps, though I feel may just add to your concience, like mine!!!
regards Kev