I was a glider pilot first and personally think it was very beneficial. In fact I'd go as far as to say that I think I'd have crashed once had it not been for the gliding! Of course I guess to get into such a situation in the first place may mean that I was stupid, but that's not the point here
How much it helps is hard to gauge as those who have will almost always say it was worth it, and those who haven't will almost always doubt it
I think it helps make you a more intuitive pilot and certainly one who is less likely to fear engine failure ... although I'd rather not test that one too often!
Why not go and do a weeks gliding and see if you find any benefits yourself. It would be interesting to see it from a pilot going the other way for a change
SS