I have an msi 560 ti hawk. I also have an antec 300 case. In the future should I add another card that is either the same or similar, or should I get a new card entirely. Keep in mind I am mind, I am mindful of a budget, which is what lead me to a 560 ti in the first place.
You should keep what you have till you have an issue with it... Then at that time see what you can get for how much and decide if adding a second 560 ti is better than a newer gen card. But until you are ready to do the upgrade it is pointless to even ask.