Here's the thing: Tom's got so many hopes, plans, and dreams that it's hard to know where to start. He's got all your usual boyish notions about being a robber or a pirate. He, like so many other kids, wants to find buried treasure. Why should we care about his dreams if they're so ordinary? Well, that's the point, really. In The Adventures of Tom Sawyer, we're supposed to identify with Tom and his desires. We're supposed to rejoice when they're met and be disappointed when they're not. And when his dreams they're just plain silly and confused? Well, then we're just supposed to laugh.
The Adventures of Tom Sawyer is, in a way, a testament to the power of the imagination; by the end of the novel, Tom has gotten exactly what he has always dreamed of having.
Although Tom is the one with the big dreams, it is Huck that ultimately comes to understand the necessity of desire.