Title pretty much says it all. The regular spots are way too crowded, the addional ones also.
I dropped specter's energy and a great marni box and almost completed it at crescents. While i did get only 20 something pity pieces at least i'm not killing green centaurs, yuks. 

Tangential question: when you exchange the 100 pity pieces for the item do you need another 100 to process it or do you keep the 100 pieces in your inventory? 

Honestly, that would be good. The OG spots would still be more popular because of the weeklies, and that's fine.

As for your question, from the description, you only have to show the 100 pieces to Merindora for her to give you the item you need to combine them.

Correct, you only need 100 pities in total. So no worries about that

Thanks for your responses regarding pity piece mechanics.