ASUS: Recommended Upgrade Components for ASUS Q500A-BHI5N01?

Hello, and thank you in advance for your experience driven insight and helpful recommendations.

I own this ASUS Q500A-BHI5N01. Overall, I'm pleased with it's performance, but I'd like to make some hardware investments to improve the overall speed, performance and quality of it. If you can please provide any recommendations on hardware upgrades, I'd appreciate it (for example; hard drive, RAM, etc..). I'm particularly interested in upgrading the HDD, possibly to a SSD, but I'm not sure how powerful of an upgrade to purchase. I'm concerned that I could end up overspending on hardware that is too powerful for the other components to handle - and therefore won't make a noticeable improvement in the performance. For example, if I spend $200 on a SSD, and I only get half the performance benefits of it due to the other components holding it back, I'd like to know that before making any investments.

I hope that what I'm asking is clear, despite my lack of appropriate "tech" terminology. Thank you so much for your help. If you have any recommendations, please include detailed models or specifications in your reply - below you'll find the specs inside this laptop:

Processer: Intel Dual Core i5-3210M (3M Cache; 2.5 GHz Clock - 3.1 GHz Turbo; rPGA)

RAM: 6GB DDR3 (4GB + 2GB)

Max RAM: 8GB

Max Resolution: 1366 x 768 (HD LED-backlit)

Touchscreen: No

HDD: 750GB @ 5400 RPM

Intel HD Graphics 4000

* Here is a link to the Laptop, which includes Specs:
ASUS Q500A-BHI5N01 Laptop Computer - 3rd generation Intel Core i5-3210M 2.5GHz, 6GB DDR3, 750GB HDD, DVDRW, 15.6 in. Display, Windows 8 (RB-Q500A-BHI5N01) (Refurbished) at TigerDirect.com