I have a two related questions:
If a question goes for a long time unanswered, what can we do to get more attention brought to it?
If it goes on for too long unanswered, can we republish the question again?
The preferred mechanism for this is the Bounty. Once you have enough rep you can set a bounty on your question (or other people's questions.)
This highlights the question, and generates interest.
Publishing the question again is definitely frowned upon - this will get closed very quickly, and will likely get you down votes.
As @paj28 commented, editing a question does bump it up, but you need a reason for editing - you must improve it, add some additional useful information etc., not just edit it bump it.
That said, you don't currently have any questions that are old - your oldest one is only 4 days old, so I wouldn't be thinking about this yet.