The Gemara gives an analogy that in the olden days when they inaugurated a new King, they used to make the coronation ceremony by a well spring. This was done by a well spring, as a sign or omen, that the king would continue to flow just like the well spring. Following the signs, in fact has an effect. Whether it does something in Shamayim like the books say, or whether it does something to the person himself, psychologically it puts the person in a sweet and motivated mood to do Mitzvot. When one eats things that are sweet, so therefore one should not minimize the Simanim that we do on the night of the holiday.

The Arizal says that when one eats the apple, there is a lot of Kabalah behind eating of the apple. So therefore certainly, one should not minimize the importance of eating the Simanim.

If one does not like to eat those foods because they are not tasty to him, or he is allergic to then, so he would not have to eat them, so long as he points and looks at the foods when he says the Yehi Ratzon. That would be sufficient. This Halacha is brought down in the Gemara and the Shul