The line about miracles not being spectacles comes from miracle principle #10 or #11 depending on where you look.
The full context is this:
"10. The use of miracles as spectacles to INDUCE belief is wrong; or, better, is a misunderstanding of their purpose. They are really used FOR and BY believers."
"10. A miracle is a reversal of the physical order because it brings more love to the giver and the receiver.
(A miracle is misunderstood when it is regarded as a spectacle.)
11. The use of miracles as a spectacle to induce belief is wrong. They are really used for and by believers."
So really Jesus is talking about the fact that receipt of a miracle requires belief to be present in the person who is receiving the miracle. Jesus is teaching about how the recipient has to want and be ready to accept a miracle without fear, otherwise they cannot be healed. "The fearful are not healed and cannot heal".
So if we are using a miracle to try to "cause" someone to believe, this isn't really going to work and the miracle isn't going to work, because the person has to believe in some way in the first place, already. Without a willingness to receive and accept it, the giver can't give it.
This is really the only way in which Jesus cautioned against spectacles. The focus isn't even on the miracles being spectacular. Whole topic of the miracle principle is talking about how both giver and receiver have to have belief, and so trying to make the miracle "produce" belief by like "putting on a show", misunderstands what miracles ARE and how they work. Which means that IT IS NOT POSSIBLE to use miracles as spectacles. They DO NOT WORK when the person doesn't believe already ie has a willingness to claim the miracle for themselves.
It has nothing whatsoever to do with telling you not to perform miracles, or for your miracles to not be spectacular, or for them to be hemmed in by size or scale or intensity or effects, or to be limited in any way, or for one to be more difficult or to fit into the hierarchy of illusions in a different way.
He is merely telling us that the way miracles WORK entails cooperation, not coercion. And that is all.
He also comments "A miracle is misunderstood when it is regarded as a spectacle." - in other words, it is only when a miracle is REGARDED AS a spectacle, that it is being MISUNDERSTOOD. Which means, referring to miracles AS SPECTACLES IS A MISUNDERSTANDING. It does not mean miracles aren't spectacular or big or literally moving mountains, it means they are being INTERPRETED incorrectly. This interpretation is once-removed from the miracle itself, and it is the interpretation of "spectacle" that is BLIND to the fact that both parties must have been consenting.
Go tell Moses to stop parting the red sea. He wasn't doing it to show off.