The idea of gaining gold per won battle is very good.
Encouraging players to play to get small bonus except just satisfaction of winning or (of course just possible
) sorrow of losing is smart and you shouldn't change it.
However, if you wish players to not be able to buy even one pack with free gold they received your way of thinking (in my humble opinion) is wrong.
Right now player needs 150 games won to buy a single pack with just 15 cards. How many hours does he have to spend on the game to receive this one single pack? Against AI, hmm, maybe just a 100h, maybe more. If that can be called "just", of course. How many days will it be for those of players who work? How many more of those who still study?
And how will it look like in PvP games? How many minutes can take a PvP game? 30? 60? Or max. of 120? 1 gold for 60 minutes of playing and (maybe, maybe not) winning is so much? Would 2 gold be so much? Doubt it.
I would say that you should WANT players to be able to buy free packs with got gold. Not because you will lose money thanks to it but because you can gain money thanks to it. If someone will get one, two, even three packs for free and will not start buying more this will mean:
1) he is greedier than you decided to be but he plays the game so you have one more active player online, thus more players and bigger community;
2) he has no money to spend on games (he is simply poor or has other reasons) but most likely will start to love you for being able to play your game and will spread this love over his friends or at least community (it's also 1 more, not 1 less player playing your game)
3) he will not like the game so much to buy it and eventually will quit
But the point is that some of players will like you more thanks to the fact that you decided not just to take money from players (and please be serious, what kind of reward you plan to give to all players that already helped you with their ideas [intellectual property
] and will keep helping you in this, next and maybe in next 20 years?) but also to give something to encourage them to play your game, not MtG online for instance or WoW.
So think it over if you see any sense in my arguements or not.
It's your choice if you, of course, read these words