Don’t forget that investing into pillar 3a gives you an upfront tax advantage, alone due to paying in.
A net income of only about CHF 74’000 in the canton of Valais for example is estimated by Comparis 3a tax calculator to save about CHF 1’800 of tax each year.
What are you going to do with these 1’800 CHF, or CHF 150 each month? 
It could increase your monthly savings amount by 10% “for free”.
Well, it’s of course not entirely free if you have to pay taxes at the time of withdrawal, is it? But 3a investments are mostly tax-free (during the savings and accumulation period), as opposed to dividend distributions from your regular non-3a portfolio, which are taxed each year. In your case, you could even contribute more to 3a, since you haven’t exhausted that yet.
In other words: similar to interest, the tax savings you make by investing in pillar 3a will also “compound” over time.
PS: @Cortana made a similar point in the other thread linked above.