I already have one 7850 in my computer right now and I am hoping to future proof my rig a little bit more by getting this upgrade and hopefully later this year get a 8350 as well. So I am wondering if this is worth the buy.
Not at all.
You can throw a 7850 in there, but there might be some bottlenecking. Either way you're going to notice a significant performance improvement though. You can always get the 2nd 7850 now and then grab an FX-8350 later to minimize the bottleneck.
I would get the second 7870 and get the 8350 when ever you have the money (if you wanna future-proof your rig an 8350 is the way to go!) also the bottle necking would depend on what games you are running like BF3 which loves to eat up the cpu would probably cause your cpu to bottleneck the 8350.
(Also keep in mind that newer games are probably going to use more cores)