They needend have bothered. The increase in money per level is so low anyways.
The gain per hour increases slowly with higher girls and for daily resets you will be ignoring Lola, Geeky and Frecly/Cherry. Resetting after Dora is around 10 per hour, Indira around 17 per hour, Ashley/Zoe/Twins 19 per hour. This assumes you will reset if you have to wait for skills/money. Since you might want to send your girls for training, you can assume 1 or 2 resets a day. This brings you in the area of 60-150 reset bonus a day. Starting with 6000 you would need around 40-100 days of resetting to get a x2.
My reset bonus is a lot lower than this, so I would get a x2 a lot faster