Go for it. What matters is enjoying the FOSS integrity as you customize to suit YOU. Whether one icon or an entire set- the result should be that when you log in, you do not feel like you are looking at dull drudgery, but like your desktop is an exciting and active place.
It's mentally more healthy to enjoy an aesthetically pleasing desktop as you work. Especially for those that spend a lot of time in front of one.
Theming also inhibits conformity and pressing users into a One-size-fits-all mould. It keeps programmers and developers attentive and productive as themes can quickly highlight problems or suggested improvements in an apps functionality.
I am not a programmer, I am a mechanic. And as one, I can tell you: Precious Screen Real Estate is not a primary concern. What is; is having your toolboxes and tools organized in Easy Access and Easy Reach. You can limit shop space, but you can never limit tools.