Either you believe you're a legitimate contender, in which case you can seriously pursue rentals, or you don't in which case any rental is frivolously flushing assets down the toilet. Period.
2nd round picks and Fasts and Kristos have meaningful value. 4th round picks, even 6th round picks have value (Callahan was a 4th, Hagelin a 6th). Are the odds great? No. But you don't waste them for what you believe is an ill-fated run. Rather, you collect more of them from the guys who are going for it in order to increase your overall odds of finding another Callahan or Hagelin, because while the odds for each individual pick aren't great, they get better and better for a draft overall, the more picks you include.
Also, if you don't think your team is championship worthy, what is the point of propping it up to win one more PO game before it falls out? All you've done is worsen your draft position. I'm not saying you don't root for your team to win - lord knows, every time the puck drops, I do. But when making deals, this current team should only be looking to the future. And if the core that's here now then goes on to surprise in the POs, that's a fantastic bonus that I will celebrate for days.