If you want to play games such as Minecraft or other games casually, a regular PC in the range of $200-400 will do that. If you want to play games like Battlefield 4 or Call of Duty Ghosts, you'll need a gaming PC in the range of $500+ will do that and will play games like Minecraft really, really well. If you have the time and want to get a gaming PC, I suggest building one. LogicalIncrements.Com is a really helpful free resource for parts.
It has been my experience that gaming pc's make the best computers if you watch a lot of videos or download media. They're built to a higher standard so they perform better in other functions too. For a good value, check out Asus computers. It'll probably handle most games while not bankrupting you.
Simple game like Minecraft, soldat, quake, or the use of a browser, will most likely not need a decent graphics card to run well. But, if you intend on playing: League of Legends, Counter-strike, Dota, Planetside 2, Tribes Ascend, or any other games from '11 to now, and possibly the future. Then yes, a gaming pc is highly recommend, especially now since games are becoming more resource-hungry. (If I were you I'd build my own gaming PC.)
Getting another PC will be just a waste of money. I don't to spend 500 or so bucks on something I can do with what already have. What's the point of all that? But I don't know. I'll leave it up to you guys to see which is more "economically feasible."
Its fine with a regular what is the difference, its not much so why not playt on a regular one, try it out and if it is your thing then maybe then maybe you might wanna have 2nd thoughts on buying a gaming pc if gaming on pcs is your thing