I took advantage of the double cash period to level up faster. It was a good chance for me as well as for many players to level up faster. It's aslo feels so good when you play Co-op Arena and you get 100.000 points in round 10!
I wish they would have kept it in permanently. I'm working on my 4th legacy and it was nice to see the experience actually pile up a little bit. Watching that tiny blip that it went up after that win was a bit disheartening.