There seem to be two bits of a thread going on here.
Thread part one - about the behaviour of the Elves. I think there could be any number of explanations as to the differences between the Elves in the Hobbit and the Elves in LotR (and indeed, they are different again in The Sil).
Within the structure of the story there is the translator conceit explanation; it is quite possible that the Elves of The Hobbit are different as the one who wrote the tale was different.
The timeframe of both tales is different too. TH is set at an earlier date, before the finding of the Ring, and presumably before the Nazgul are as active as they are in LotR, going about Middle Earth and terrifying the populace - and making Elves feel far less frivolous.
We meet different Elves in each book. Elrond is the one constant who seems much the same in both books. In LotR we tend to meet Elves higher up in the social order, and hence more burdened with serious issues. And by this stage burdened also with the immensity of the news that the One is found and being carried about Middle Earth, and that Sauron is building his army.
Maybe the differences could be accounted for by the different types of Elf. Galadriel is one of the Eldar, while those in The Hobbit are Silvan Elves, of the Nandor. Of course, Legolas is one of these and he is not overly given to frivolity, but he could be much better travelled than his father, maybe he is more aware of the wider world and how its concerns have an impact on his kin. The Elves of Mirkwood are quite hostile to outsiders and would probably not be keen on travelling far and mixing with others, but Legolas seems to act as his father's messenger, either through his father not wishing to leave Mirkwood or being forced to stay and defend it.
Thread part two - Elrond knows about Bombadil, and the Ents must also know about him if they know about the Old Forest. Tom is the 'oldest' of all, so there is a high likelihood that he has met the Elves, and probably shared a few songs with them. Maybe they made him his boots?