The resell value of manga varies. Popular series that are out of print or have collectible features can be valuable. However, most mainstream manga might not have much resell potential unless they have some special attributes.
Comic book resale can be hit or miss. Well-known series with dedicated fan bases tend to have better resale potential. However, it's not a guarantee and a lot depends on the specific comic and the current market demand.
Yes, it was an original story. The concept of 'The Purge' introduced a unique and disturbing dystopian idea of a society where all crime is legal for a set period of time. It had its own distinct plotlines and themes that hadn't been explored in quite the same way before in mainstream media.
No. 'The Purge' is a work of fiction. It's a creative concept that imagines a world with a very different social structure regarding violence and law. There are no real - world events where a government sanctions a period of lawless killing and mayhem like in the movies.