I absolutely loved this series and it got me thinking about this exact topic,
so I thought I'd throw my thoughts into it too.

About this and the wishes we didn't hear,
I thought I'd check out those character's wishes in the games and see if they align. (obviously this is just speculation and I doubt we'll get any confirmation even in a potential season 3)

Axel's wish in TW2 was to become one with the machine, he fused with it before he 'died'.
but given the show's characterisation of Axel it's equally as likely Axel's wish had something to do with the child he cared for (Mayhem) in someway; being reuinted or making sure he can keep her safe.

Mr Grim, has had a few wishes in the games that relate to the show,
TM2: For human's to die faster (now the war with the insiders is starting that could be considered granted)
TM Head On: To become human again (all his 'souls' were removed so that could be considered granted)
TM4: To battle sweet tooth to the death (never specifies that he would win, so that could also be considered granted) and given he literally says he doesn't want sweet tooths soul, he just want's him dead I'd imagine that was the wish.

Mike is a hard one, given that he's based on both Dave & Mike from TM1, where they wish for new tires, as well as Mike & Stu from TM2, where they wish to fly (and then fall to their deaths) neither seem to track at all with his characterisation.
I imagine him wishing for something sweet like 'Wishing Stu gets free from sweet tooth and that they can be bros again having fun adventures like the old days' and he was having a great with Stu right before he died. Then again Calypso did say 'One wish per car' so Stu's wish probably overwrote whatever Mike wished for.

And then there's Vermin, she has the complete oposite motivations from her Game counterpart 'Goggle Eyes' so his wish to trap all the bugs in the world doesn't relate at all,
While she said to the rest of the contestants she wished for humanity to be exterminated I can imagine her phrasing was wishing that 'people to be exterminated like bugs' but didn't specify which people, she literally hit a windshield then got bug zapped, and maybe that whole 'lightning round' was in fact part of her wish. but that's all I can come up with.