The systesm of kobudo study from Okinawa utilize weapons that can be found in many other SE Asian cultures. The Chinese crutch is similar to the Tonfa. The Sai are found in other cultures. The Kama is a unversal gardening tool, the same with the Bo, found everywhere in the world.
Kobudo seems to have developed mostly in family or town systems of study. By the 1920's it was on its way of the big decline but individuals like Moden Yabiku, Mabuni Kenwa and Taira Shinken began working to save those traditions. As time passed others such as the Yammani ryu, Matayoshi's Kobudo, and other more rare systems began to be shared pubically.
Things always changed. Today some Yammani practitioners have added Sai, where Yammani originally was just a bo system of study.
In the past 50 or so years some of the Karate systems began to add kobudo more significantly.
Kyan Chotoku only incorporated one bo kata (Tokomeni No Kon) but in time some of his students also trained with Taira Shinken and various other kobudo studies were added.
When karate transferred to Japan, Funakoshi Ginchin did demonstrate sai and bo (his father was a bo expert) but those arts didn't fit the needs of the University students he was developing, nor did karate grappling studies. Japan had its own old weapons traditions, and developed judo from jujutsu, so why add what the Japanese weren't looking for in any case.
Functionaity can always be discussed, but in recent history the use of kobudo for significent self defense is non-existent.
The most obvious value to long term (20+ year) kobudo study is the secondary value it imparts for strength, grip and etc.