It is better to make a second post since no one has posted in a while to rephrase the question. You should avoid posting empty content like just the word bump. No point in making a new thread that is basically doing the same thing.
In terms of bumps, necros, and double posts it is usually more about context of the situation you are doing the item in. For a necro you should only necro a thread with an actual relevant post that wasn't covered and avoid flaming or causing trouble with the post. For bumps like I mentioned above it is better to rephrase a question or rehash something then to make a post without any real content to it. Double posts are permissible to a point as long as it is not habit. An example would be the rare double post bug or if you are posting to a thread that hasn't had a response in a while. I use rule of thumb for myself for a week or if new valid content has showed up and no one has commented or posted in three days.
edited 6th Jun '15 11:29:23 AM by TuefelHundenIV
Who watches the watchmen?

So, I have a really old thread here where I asked a question, but I still haven't got an answer. It's still on the first page, but it hasn't been answered in months, and I think I know a better way to phrase the question I asked.
So, should I bump the pre-existing thread, or should I make a new one with my question expressed better?