Another thing to consider is how set you really are on putting words to the music. Maybe its just me, but I often times find it very hard to lower the music enough to let words slip in...Thats not to say a song written with lyrics cant very very full and complete sounding, but as someone else mentioned in this thread it draws attention away from the performance piece. So I guess it would really depend on what you want to showcase, your lyrics, or your playing capacity.
Generally think about it this way...when you listen to a piece, and they go into that really amazing instrumental section...the words trail off. And obviously this is intentional, as the instruments are going on showcase rather than any words. I personally see this as a completely viable way of writing a complete song, and words are something that can be left to every individual listener.
In that train of thinking, anything you write, lyrical or instrumental, will be at the mercy of every person who ever hears it. Thats not a bad thing, or a good thing. Just a fact of the music. When I am asked why I dont put words to my music, the only thing I can say is I would rather they decide what the music is worth, and if they want to put words to it, they are more than welcome to.
End of the day, it comes down to expressing yourself in the best way you can. If that involves lyrics, so be it. If not, you're still golden.