[Melilot Brandybuck]

I think that the apparent light-heartedness of the elves in this chapter reflects Bilbo's first meeting with them, and how they appeared to him, through his eyes. After all, the ring was yet to be discovered, with the troubles that occur in LoTR some time off. Bilbo was probably only vaguely aware of the history of the elves, if at all, so to him they were creatures of wonder and mirth - the troubled and sorrowful side of their existence was not obvious to him on this first meeting.

I think it's right that they are portrayed in such a way. As this was my first introduction to ME, if Tolkien had depicted them as melancholy and brooding, I would have thought, "What's up with these stupid navel-gazing elves? They live in this wonderful valley with food, wine and song a-plenty but they're wandering around with faces like a wet weekend..." As the story of the elves unfolds in LoTR, you learn that in fact the elves have a troubled past and face a bleak future. But at this point, we as readers aren't aware of a ring, nor is Bilbo, so it's enough for us to know that elves are a light-hearted and wondrous folk who are willing to help a bedraggled bunch of hungry and forlorn travellers.