One example where doubling content was handled well in my opinion was the punchbowl fountain. It appeared first in Luxury party, then it got reused for City living, although not to be uses freely, but only during festivals. So if you already had Luxury party, you didn't get an item you had already payed for twice, but the same mesh with a new function. And if you only owned CL you got to try a demo version of the fountain as an incentive to buy the stuff pack.
I hope they'll one day do something similar again and offer a winter vacation GP with an eternal winter for those of us who do not want Seasons... but might, after we bought their GP. Some interactions like snowball fights would still be exclusive to Seasons and owners of Seasons would get to use, for example, skiiing and snowboarding everywhere, while non-owners could do these activities only in the new vacation world.
