I'll start my post by saying #1 -- I dont think the Blues are trading Parayko.
That being said, anyone who "balks" at Parako's $6.5 x 6 remaining, should only be reminded about how badly so many fans wanted Alex Pietrangelo, and would have happily offered more than the $8.8 x 7 that he eventually got.
The reality is, if the Leafs are going to be a truly contending team, they need to stop leaving massive holes in the lineup "to be filled at the deadline". The deadline is an opportunity to acquire a guy that is a first liner on antoher team to give you depth. It's not when you should be shopping for a guy to play on your top pair.
Yes, the contract has the potential to turn sour, but with reasonably expected cap increases, he does not need to be a #2 defenceman by the end of it. Acquiring Parayko instantly gives the Leafs a bonafide, and locked down top pair. Let Brodie walk or take a paycut in the offseason, and you've got a solid foundation of D to build off of.
In an ideal world, the Parayko deal would include Niemla and not Liljegren, but I'll go back to my first point on that. St. Louis needs to rebuild their D, no question about it. The challenge is, they've got Kyrou/Thomas, and a bunch of young forward prospects either in the league, or coming very soon. They're going to want defencemen that are already in the NHL to give the right "age bracket" to pair with their forward prospects.
That being said, I'll go back to my first point. I don't think they have much interest in trading Parayko. It makes more sense to shop Faulk, Krug and Leddy.