What functionality is missing? What is unsatisfying with the current situation?

  Currently, as soon as the suggestion is posted you are unable to post another suggestion until it has been closed, which is a good system.
However, in cases where it is clear the suggestion will not be accepted (such as reaching a threshold of -1000 points), the user is prevented from tossing out the suggestion and uploading other suggestions.

How does this feature request address the current situation?

  By either allowing the submitter to manually close a suggestion or having a simple automated system to discard 'bad' suggestions, users will waste fewer coins on 'lost causes' and the suggester may be able to bring up a new topic.

What are other uses for this feature request?

This may also slightly reduce manual labour required.