I agree with you here,
Mithadan. Bilbo becomes brave, but also
resourceful, without which his bravery would count for little. The dwarves start to treat him with respect, after finding out that he escaped the Misty Mountains
on his own.
When he met them again, they and Gandalf were debating going back to rescue him.
As you said, it's a prelude to him dealing with the spiders in Mirkwood, and successfully rescuing the dwarves from the Elvenkings cells, all warming up to him voluntarily deciding to go and confront Smaug.
The Hobbit certainly becomes a more 'adult' tale from Chapter 5 on, one that Tolkien is able to later integrate into the history of Middle-earth.