Has Ayew been a good buy? He supposedly broke thier wage structure, cost them a £10m signing bonus and he's managed...8 goals.
Payet is being presented as a revelation...he's not. Everyone knew about him, no one was interested because he had an awful reputation for partying and not being professional - he once attacked his own captain on the pitch when at St. Etienne, only last season he got dropped at Marseilles for not putting effort into training and got banned for abusing the referees. There's a reason the France manager hasn't been picking him, because he's trying to stay away from the drama they had at the 2010 world cup and 2012 Euros.
Every club in the world knew who Payet was, they just didn't want to Spend £15-20m on a 29 year old guy who could explode at any minute, and West Ham did, so they tried to sign him all summer and failed, but then Marseilles hit some big financial troubles and had to offload him fast for a knock-down fee. They got lucky and Bilic has gotten the best out of him.
I'd much, much rather pay £50m for a 23 year old KDB.