They really don't, you're getting free money in-game and another Rockstar game depending on which one you choose. It's worth it because you're still getting stuff you wouldn't have gotten with just the base game.
Skial
Chance
Sir Cakez
The problem that I see with it is that there is no option for just the base game. With all the complaints about hackers in GTA Online, I don't know how much I would really want the money.
Cowboy Crow
BOO FUCK YOU ROCKSTAR AS I PULL OUT MY WALLET TO BUY YOUR GAME AND THEN BOYCOT YOU.
Chance
I have only ran into 2 hackers in my time playing online, a lot better than most games. Worth every penny imo.