Board Thread:Game Discussion/@comment-31526827-20171030020306/@comment-31433854-20171031154030

The rewards would have been 100, but the car's share would only be 25. You can't ignore the contribution of the other three cars in Week -2, Week -1, and Week 0.

Even ignoring that and sticking with your example, buying the GSV, Vulcan, and FXX-K would still be 2300gc to get back 700, so I'm ahead by 1600gc by not participating :)

WTTT can be used to subsidize some of the cost of going for 100% but it is not effective as a stand-alone source of gold. To keep picking on Fandoom, he is using the extra gold from WTTT to advance an alternate goal (100% garage). This is reasonable. However, if you have no other reason to have the 919, than that 950gc would probably better serve you elsewhere.