I've been having similar issues. I think that some of the small things we may think of as sellers, and knowing our products so well may not be what the buyer searches for.
What I've taken to doing to check if my tags are relevant is go to the search bar and type my first word of my tag and see what pops up. For example I typed in crochet to see what the most common searches for and saw that bag or purse was part of the top, so I know that if I tag my listing with those keywords I should be more relevant to the buyers searches. Not everyone knows what special technique or material you may have used, so including that might not be the most optimal use of your tags.
I don't see why repeating the listing title but changing for color if the item is essentially the same, it might actually help get more hits, I would think.
Hope this helps!