I have 7.1 headphones, and I can't tell a difference between 5.1 and 7.1.
I assume it would be similar for a speaker system.
Headphones are not a particularly good way to judge surround sound. Honestly, with headphones there is hardly a difference between stereo and 5.1.
However, I agree that there is not a huge difference between 5.1 and 7.1
As far as whether or not it's worth the trouble? Well, if you can and want to do it then why not? But would it be a huge night and day improvement? No.
Personally, if you want to notice a big difference in sound, I would invest in the highest possible QUALITY of speakers rather than just going for more quantity.