[iMore Question]

Here is an overview of my Mini:
Hardware Overview:

Model Name: Mac mini
Model Identifier: Macmini3,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.53 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 3 MB
Memory: 4 GB
Bus Speed: 1.07 GHz
Boot ROM Version: MM31.00AD.B00
SMC Version (system): 1.35f1
Serial Number (system): H095047G9G7
Hardware UUID: EAACE2BE-8806-541A-BF27-B663FEADCC80

I am not a 'gamer'. My uses are internet, photos, music, and some iWork. My machine is slowing down. I recently added MACKEEPER.

[kch50428]

Go Yosemite... It's running quite well on my MacBook Pro circa mid 2008...

[nikkisharif]

Agreed...Yosemite runs pretty darn good!!

[Algus]

My machine is slowing down. I recently added MACKEEPER.

Well here is your first problem. I won't get into the whole "Is MacKeeper worth using" debate but I do recommend this article from Cult of Mac so you are at least familiar with it. I recommend uninstalling it, especially on an older system that is in precious need of resources.

It is very important to keep your system as updated as you can. Older operating system versions do not receive security patches and updates from their developers (in this case Apple) so having Mavericks or ideally Yosemite installed on your system means you will continue receiving security updates.

Doing a clean install of your operating system as per this article can help clean any garbage out of your hard drive. This will wipe all your data so obviously make sure to back up your important files and documents.

You shouldn't ~NEED~ to buy any new hardware to get your computer back up to snuff but you can also buy more RAM or a SSD for your computer, both options that will improve the performance of your system without you needing to buy an entirely new computer. I recommend Other World Computing if you decide to go that route. You don't have to buy anything from them but they cater to Mac users so they are good to do research at even if you don't plan to buy from them.