I haven't deleted any cities but, suppose that I had one that was a hot mess or one that I grew bored with and wanted to start a new city. If I were to take a few weeks and use all of the collections and current FP bank investing in P1 spots on a selection of GBs I could then delete the city and start over with a new city on the same world. Some time afterwards that new city would recover the previous investments along with an assortment of BPs and medals. Seems like a novel way to get a kick start in the new city. Full disclosure, I have no interest in doing this. My interest is purely academic.
Even with the kickstart, you'd still be way behind where you were. So at best you could view it as a very high price to de-age. It would always be "better" to fix your hot mess than start over.
If you're starting over for fun, sure you could do that
But I don't think it'd be that big a lift to have extra FP packs rolling in, if it still works. And since you'd be behind where you were it'd be hard to call it exploitative.
As a point of comparison, in a 1-week old world I started to test something I have ~600 FP in packs already - primarily from break-even-ish investments of FP the event threw at me. If someone wants to go through the trouble to delete and restart an advanced world and hope that say 10k FP bounces back to them sometime shortly after 2 weeks later, I'm not sure why it should bother me. Hardly seems worth the trouble considering the time that went into creating that world.