I think the silliness worked in context. The monster conference is something goofy, buy still easy to appreciate on many levels. First of all the notion of three animalistic monsters teaming up to fight one great threat was bonkers and Sekizawa knew it. So instead of trying to play it straight he used the genre's qualities to get away with the anthropomorphizing of these beasts. It works because this is the only genre that can get away with it and land safely.
Furthermore, the monster conference really is right in line with Honda's constant theme of unity. He spent a lot of time in previous movies, both Godzilla and otherwise, pushing characters and mankind to band together against an overwhelming threat. Here he does it with the monsters. We already know Godzilla and Mothra are enemies and this film would've made a great case for Godzilla and Rodan's rivalry had King Ghidorah not shown up. Three monsterous enemies band together to fight a great threat. And what's more it's not Mothra's words that convinced them, but her actions. Honda's never been much for political bickering-- As he made clear in the original Godzilla. It seems that even when Mothra's at the podium he doesn't think it's worth much.
I think the real issue with this movie is how rushed it was. It's incredible Honda and co. can make movies like this on such a asinine schedule-- As much as directors and special effects men complained about the rushed schedule in the Heisei and Millennium series, they never had it as bad as the crew members in the 1960s and those movies were much better. Still, the rush job shows in some places with Ghidorah.
The editing sometimes doesn't makes sense. At one moment we're in a hotel with Princess Salano and her assasins at night, then we cut to Professor Mirua at the camp site during the day. This wouldn't be big deal if it weren't for the fact that the very next scene is the exact same setting with Salano... It's either an editing goof or the assasins were pointing a knife at her in that hotel for 24 hours. It's not the latter...
Love this movie regardless though.
"'Nostalgic' does not equal 'good,' and 'standards' does not equal 'elitism.'" "Being offended is inevitable. Living offended is your choice."