XLR cables, worth buying higher end?

Yes look at Tara or Purist both great sound.

Maybe? 
Buy a nice quality set of used cables and set of the cheapos and compare/contrast. 

It really depends on you equipment, your ears, how critically you listen. You need to have a pretty good system to notice. Now, it will be noticeably louder... but not necessarily a noticeable difference in quality. The volume increase makes it really hard to compare for quality.
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I used single ended for 40 years. It was only when my system got to really high level of performance with all ARC stuff... who recommended using XLR as the have all balanced internal design that I finally converted. 

Yes and...

I noticed the use of XLRs result in increased signal level versus RCA.

The basic (better cable and mogami) versus higher end (kimber) was noticeable for my source components.   The impact was less than the RCA to XLR.

XLR lowered the noise floor on my Pass XP-20 to XA100.5's. I wouldn't spend to much to try and see if it makes a difference on your equipment. I used these https://www.dysonaudio.com/collections/facemelters.