I've asked questions in the past that have gone unanswered or have not had sufficient answers, would it be unethical to repost my questions to try to get an answer another time?
Posting the same question anew just to get more attention is not acceptable behavior. Please do not do this.
If it is noticed your questions will be swiftly closed as a duplicate, likely it will also be downvoted and usually some users will complain.
For acceptable ways to draw attention to existing questions see How to grab users' attention on an old question? (although one suggestion, namely to edit, may have been more effective when that answer had been written then it is now.)