My general rule of thumb is that most octos shouldn't need toys or additional enrichment if their tank environment is good enough and is changed frequently. I have never given any toys to my octos and they have all done just fine and lived full lives.sooooo do we have any news regarding toys? any new insights since 2011?
For me, "enrichment" consists of mimicking the animals natural environment, rather than giving them toys that are made for humans or dogs etc. An octopus would likely never experience a Rubix cube in the wild, nor would it likely encounter a wiffle ball or other toys that people commonly give to octos, so the toys are obviously nonessential for the animals wellbeing.
I think its pretty obvious octos love to touch and manipulate objects so it is important to have things in their tank environment that they can manipulate and interact with. If you decide to use a wiffle ball to achieve that, then that will likely work for your animal. I know some people use sterilized clam shells or small flat rocks or pieces of PVC tubing, which I think is closer to what they may experience in the wild.
While it is impossible to know for sure what makes an octopus most comfortable in their tank, I do think the best enrichment comes from a well mimicked natural environment, rather than an abundance of toys.