I'm not sure Couture is worth that much on the trade market, anyway. If you compare him to Karlsson, he's older, also injury prone, signed for the same term, and nowhere near as impactful when healthy, and Karlsson returned a 1st and a bunch of cap dumps.
Now, in any comparison of one player's value to another, you have to remember that trade value is not linear to expected return based on some set market, but is extremely volatile. This was my objection to the statements about the trade value of cap space in comparison to the Marleau TOR-CAR trade - just because Marleau returned a 1st, doesn't mean that every trade to clear up $6 million in cap space will return a 1st. Trades are not a large-scale money economy where prices are set by the invisible hand - they're a very small barter economy where prices wildly fluctuate based on whether anyone has eggs right now.
However, given Couture's talents, contract, and drawbacks, I'm not convinced he would actually return a 1st - especially if we don't want to retain any. I think we'd get some cap dumps and something like a 2nd or a mediocre prospect (someone like Emberson or Makiniemi or Robins - probably not going to be better than depth, and probably less than a 50% chance to hit even that).