There's a difference between signing a stop-gap versus trading for one. If you can upgrade the team for free in free agency by signing Weiss? Why not?
It upgrades the team AND gives us the option to trade a guy like Grabo and get assets in return. That's win-win in my books. Upgrade current NHL team + add some picks/prospects for Grabo.
Trading for a #1 guy? Thornton is literally the only example of a legitimate franchise centre that was acquired via trade in the entire league. It simply does not happen on an even remotely regular basis.
I agree with you but, Carter to Columbus and M. Richards to L.A. would be the closest things. That being said, neither were #1 in Philidelphia and Richards wasn't even the #1 once he made it to L.A. Both guys can be argued to be top 30 centers in the league though and would easily be number 1 here.