I was in a similar situation a couple of years ago (artist, EU, full time freelancer, kleinunternehmer) and also asked myself: is it worth it? For me yes. I'm not planning on moving abroad anytime soon and It makes sense for me to start paying into pension as soon as possible. Being insured through the KSK also made it possible for me to switch from private to public insurance and now I pay the same I used to pay for private insurance, but for health insurance AND pension. Besides, the big bonus for me is that you pay according to your yearly income; so if you have a weaker year, you don't have the burden of paying so much insurance.
So maybe what you have to think about is: am I planning on staying in Germany? If yes, do I want to pay into the public Renteversicherung, knowing that when the time comes most probably I will get less money than I paid into? Do I want to switch to public insurance - this is good for when you want to start a family, even if in only 10 years, plus you avoid ever increasing premiums?
if your answer is yes for two of the above, I'd say go for it.