It's worth noting that Jesus is not necessarily rebuking the disciples. On its own the question "Don't you understand this parable?" is neutral and ambiguous. Maybe Jesus is telling them off; maybe he's feeling disappointment or surprise that they don't understand; or maybe he's just making sure he understands their response. These are all possible underlying reasons for the question. We need to be cautious about reading one or other context into the bare words.
As for the main question, we are not meant to look within this parable for buried clues that explain the other parables. But there is a more natural sense in which this parable is indeed a key to the other parables.
The parable tells the story of a farmer who sows seed, and how the seed germinates in various ways according to the environment. And Jesus interprets this as the word of God which bears fruit in people's lives variously according their human environment.
Now Jesus himself was in the role of the farmer. He was speaking (or sowing) the word of God into people's lives, and this was often done in the form of parables. So here Jesus is in effect telling a parable about what happens when he tells parables. If the audience lacks the spiritual insight for this parable, then for them the word is like the seed that fell on poor ground. But if they understand the story, it shows they are receptive to God's word. We could describe this parable as a litmus test. How we respond to this parable will be reliable indicator of how we will respond to Jesus' other parables.
