I'm glad that the ability to delete a node is not widely available. Deleting nodes should only occur after appropriate consideration (whether formal or not). Whacking nodes can destroy the context of a conversation, rendering the work of respondents much closer to useless or nonsensical.
If you inadvertently make a duplicate post, it's probably productive to check the ChatterBox and ask for help there. A janitor may well be able to do something productive. At the least, you could probably find someone to consider the duplicate for deletion.
Another way to deal with a duplicate is to edit one into an entirely different post, since you can change the title as well as the body. Look at it as a way to get twice the XP! *grin*
Your proposal is intriguing, though. It might be interesting to examine just how often a node gets deleted (and why) to discern how much demand there might actually be for this feature. How many deleted nodes would have qualified for poster-deletion under your proposal (ignoring the minimum xp requirement), and how might they have been grouped by the then-current xp of the poster?