#1
I've recently learned Coheed & Cambria - Welcome Home, I started out with the tabs on here, but quickly learned that, in one or more places, they are all wrong (I know I sound like a jumped up arse who thinks he's better than everyone else, but hear me out)
I went on to learn it by ear where I could, and using a video tutorial for parts of the solo that I couldn't learn by ear.
I'm sure that I have it at 99%,maybe 100, which is more than I can say for tabs on here, I thought I'd make my own tab for the song and post it, but seeing as there are already 7 or 8 tabs, is it worth it? I mean, will my tab be rejected because of this?
I was thinking that if it was approved, if people thought it was correct, they wouldn't reject it...
#2
There's not really a definite answer for this because UG rarely cleans up bad tabs and for popular songs may reject new tabs even if they're good. Also keep in mind that indeed almost all tabbers think that their version is correct and others wrong, transcribing is a bit subjective without second opinions and people definitely hear different things and sometimes things that aren't there, etc.

If there are several 5 star tabs of a song already, it will almost definitely get rejected - even if it's near perfect - so in that case it's a waste of time.
If there's no great tab yet and you believe yours is significantly better, I'd say go ahead.
However, if you only have small corrections, such as a few notes in a riff or solo - they prefer that you post it as a correction under an existing tab.

There's still a chance you'll get reject votes in TPA because people like to vote reject without even looking at your tab when there are many versions. Tab moderators and the "WTF, Where's my tab??" thread in the contributions forum can help you out in these cases - but like mentioned - you should only tab if there are no 5 star tabs and you strongly believe yours is worthy of it, which if you couldn't figure out the solo might or might not be the case.
GL