Should I reformat my hard drive?

Hi,
This is my first post on the Apple support community so please forgive me if there are some formalities or standards that I didn't follow.

I've been doing some research on formatting hard drives, something I did annually on my previous Windows computer, and the consensus is generally that there is simply no need to do so for OSX enabled machines.

However, I have been having some performance issues with my 2011 MacBook Pro (I5, 10GB ram) recently and maybe the solution is found elsewhere than wiping the hard drive.

My first episode of performance issues was simply due to a lack of RAM. Last year I upgraded to Mavericks and found that the demand for memory was greater than the measly provided 4GB that came stock with my computer. I bought an 8GB RAM stick and replaced one of the 2GB sticks and now have 10GB of RAM. Everything was fine until I upgraded to Yosemite a few months ago which worked fine at first but eventually the performance started to decline. I don't think it is a memory issue as I have an app that keeps track of how much I use and it usually shows I have about 2-3GB available, with all the applications open that I use on a daily basis.

Around this time I also tried to partition 50GB worth of my drive to install Windows on. After a few failed attempts (the process would simply freeze at about 80% complete) I decided to run a disk check to make sure my hard drive is working fine. After running the check it returned that there were some corrupt areas and when I tried to repair them, it didn't work. I decided to ignore it and put off the Windows installation but now with the significant performance depreciation, it's much harder to neglect.

I've tried many things such as resetting caches, using the "purge" command for my memory and simply trying to clean up files on my hard drive. I've tried a few programs that promise to "clean your mac" and whatnot but as I suspected before I installed them, most of them are either gimmicks or ask you to pay.

My current proposition is to transfer files I want to keep to an external drive, wipe my drive completely and go from there. For now, it is a worst case scenario as this process is quite time consuming, hand picking which files I want to keep and then wiping, so I've decided to turn to the support community for any advice.

I don't know how relevant this is but I've noticed that when I use gestures to either show the desktop, bring up mission control, or show all open windows, it tends to do so but it lags and performs a rough transition, rather than the seamless one I remember having when I first installed Yosemite. On top of this I occasionally get the spinning beach ball which I used to believe only meant there isn't enough memory for the current task you're doing but now I've also been informed that it means there's a hard drive issue screwing with the current thing you're trying to perform. This happens regardless if I have any running applications or not although with no applications running, the transition is slightly smoother but the roughness is still evident.

I'm not sure what additional information or visuals I should include to help you guys to be able to help me so please just let me know and I shall post what is needed.

Thank you to anyone who can help