I got impatient being repeatedly one win away from Legendary, and not having the coins to upgrade Minion Horde to 12, so I spent $5. Suddenly I've jumped from max trophies of 3787 to 3990!
I wonder if there's some algorithm in the matching that gives you a break after you spend cash, or if that was just a *really* good upgrade.
If I'd waited a week I could have spent nothing, but being so close for so long was driving me nuts.
Upgrading a single card can change the interactions with so many things. Upgrading a couple cards generally helps me hit a new high. Upgrading my crown towers to 12, archers to 13, skeletons to 12 and ice spirit to 12 within a few weeks of each other took me from 5k to 5.4k a little while back.