I don't agree that you should necessarily feel smarter by speaking multiple languages. The health benefits are well-established. For example, bilingualism is known to delay the onset of Alzheimer's, though the strength of the effect is dependent one's use of those languages (actively speaking vs passive knowledge).
I suppose you could liken it to eating nuts more regularly. It might not make you feel healthier, but physiologically it is doing that.
That fact about multilingualism helping delay or reduce the chances of Alzheimer’s / dementia is cited pretty often.
I’m willing to accept it, but I’m more skeptical of multilingualism actually making one smarter or otherwise more cognitively capable.
And that’s a good analogy about eating nuts. It’s possible that while acquiring a second language could make you smarter, it might not subjectively make you feel smarter.