Buy into second pillar or not?

We like stability and safety, and we earn a lot. My wife's pension fund as well as my pension fund both have too much money and offer an average of 4.5% interest for this year. Both pension funds are large and stable. My pension fund offered even higher interest rates to get rid of excess money only 2 years ago.

We both have "gaps" in our second pillar due to long studies and high incomes, so we are able to buy in. Do you think it's okay to put a couple of grand into the pension funds, to take the nice and safe % this year and with regard to locking it into a regulated and pretty save (even though on average not as high as, let's say, pure stocks) return long term? It's not like we're going all in on stocks as an alternative, it's more likely that the money will just continue to pile up in an almost-zero-interest savings account. Looking forward to hearing your thoughts.