Should I upgrade or buy new?

[Sinistrari]

I was thinking it may be about time to replace my Samsung Series 7 laptop but would just replacing some components be just as good. I'm not really having any issues with the machine. Just feel like it's about time to replace some outdated hardware. I primarily just want to prolong the life of the machine but, seeing improvements in performance would be welcome. I use the laptop mainly for work which can put a load on it from time to time. I run the three monitors (including the laptops') and usually have may things going on on each all at once. I enjoy gaming: Diablo 3, Bioshocks, WoW, ESO, etc.
Out of the build below, what are some upgrades that would be the biggest bang for my buck?

i7-3630QM
AMD Radeon HD 7870M
8gb DDR3 1600mhz
SAMSUNG_NP1234567890
Western Digital 1tb 5,400 rpm

 

[Maarsch]

Well, your issue is "laptop"

They're not the easiest thing to upgrade. You can basically add RAM/replace and switch that HDD for an SSD.
The SSD will most likely be the biggest bang for you buck.

 

[ThomasKK]

You could change your HDD to SSD disc for much faster loading times (~5-10 times less waiting for windows to boot up), but it has some cons:

1. It is expensive
2. Higher capacity SSD discs are, again, even more expensive

If you don't use all that 1TB size HDD, you should consider ~480GB SSD upgrade kit for a reasonable price. If you're not willing to lose space, 1TB SSD will be around $300.

 

[dudeman509]

A SSD upgrade will make that 4-core i7 feel immensely more responsive.

But that's about all you can do besides add RAM if you're going close to 8 GB used regularly (I usually don't come anywhere close with my laptops).