Can't say if it'll be worth it or not until you've played through the original game. PoP seemed to have been a "love it or hate it" type game. I liked the game, and don't regret the $10 I spent to get it. The Epilogue DLC will add achievement points and about 2 hours of gameplay to the game (original is only about 10 hours total). It was made to address a lot of the criticism the original game faced, mainly that it was too easy. Similar to the original PoP, it has little to no replay value though, so it may not be worth it to some, even if you liked the original.
It also changes the tone of the ending from the original game. So if you skip the Epilogue, you may be a little confused come PoP2.