In a keeper league I think I would trade Gaborik to get Giroux, which is basically what this deal is since it's a keeper. It's really close, but I think selling hihg on Whitney is a great plan, and Gaborik is far too injury prone, not too mention the inconsistencies as of late, for me to want on my roster. WHitney and Lidstrom are both on their last legs... if this weren't a keeper I would say no way.
I think this is the last time you can get Giroux for a "decent" price, so I would pull the trigger. I too am a huge fan and am willing to overpay for the players I want. So, as long as you aren't in contention to win this year then I would make the trade.... you only lose out this year, IMO.