So my goal lately is to get my created player (Mickey Mantle) jacked up. So instead of spending my stubs on packs, I invested them in these missions. After all was said and done, I sold all the guys earned from the missions and in total I think it cost me around 8k in stubs. Since you earn a 10 pack of cards that I was going to buy anyway to feed Mantle that would have cost me 10k stubs, it was already worth it, Plus in feeding my player to complete the missions my created player got much better and got some XPs. So win/win. I just had to invest some time in it. Of course, this is based on the current market today (the main factor in the market being what you can sell the earned players for), but I would recommend going this route if you are planning on purchasing packs. Especially if you've already completed 2 or 3 of the level I missions organically.
Ok, I'm off to open my packs to see what crap I got.
PS. Don't be a glitch bunter. It makes the game worse for everyone. The game is supposed to be fun, so don't be a prick.