Indeed, it is quite disappointing that Princess Astrid did not wear any tiara, although she owns at least one and could borrow other ones from her mother. Even more since she is not only a royal princess of Belgium, but also the wife of the claimant to the Italian Ducal throne of Este-Modena...
As for Queen Paola, although King Albert II and she have maintained a constant low-key profile since the abdication, she could have made an appearance at this particular State banquet, considering her Italian origins. But maybe King Albert's and/or her own heath condition are now quite poor to be able to bear long ceremonial dinners in the evening?
Queen Mathilde looked regal and lovely with her Laurel diamond tiara and her modern diamond tassel earrings (though the classical style of the tiara and the Art Déco style of the earrings do not match successfully, IMHO):
Earlier in the day, during the welcoming ceremony in front of Brussels Royal Palace, Queen Mathilde gave us a good view of the sapphire and diamond earrings that Crown Princess Elisabeth had worn at Grand-Duke Guillaume V of Luxembourg's inauguration a few weeks ago:

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Poor in jewels….
No tiara for Astrid….
No Italian Born queen Paola.