An old MBP of mine was having battery problems that it couldn't hold charge that it had to plugged to charge all the time. Basically it became a desktop rather than a notebook.
Even though it's speed was alright, I know it could be much better with an SSD. Also ditching the CD-ROM for an HDD sounded like a great idea since I don't rely on CDs anymore.
The repair process was excellent. It was a lot of fun.
Everything went as smoothly as it can be thanks to iFixit's great manuals. They explain something so clearly but with great detail as well that you don't run into any problems at all.
If you're thinking about making a repair to an old device of yours or you just want to bump something a little to a better state, then you may blindly trust iFixit.
When you combine all these manuals and their most excellent shop with their quality of service, there remains no reason not to act on your repair.