Excelsior

I know that the best quality i can get out of tailoring would be to wear a masters tailor suit and craft with an eth sewing kit

what i'm curious about is
if i have a +60 blacksmith hammer and a platinum kit, that puts me at 180 blacksmithy (able to craft any item of any ore type with exceptional quality without fail)
by adding a master's set to that (+30)
this will put me at 210 blacksmithy. my question is, will the items be a better quality with that +30 or does it not matter since i'm already crafting everything exceptional no matter what.

short answer is yes they will be marginally better, but since the properties are random getting a "by how much" measurement is tough if not impossible

Having a full set of + blacksmithing gear you can craft all plate armor without using a +skill hammer. That's the main difference. I'm not sure about some of the custom weapons, etc though.

And the higher your skill the better chance you have to enhance something (like adding gold for some extra luck), although success rates at 208 are still extremely rare.