Polish increases customer lifetime value.

This means really little in itself.

Can your customer switch to another product, yes or no. If no, then polish won't happen.

Do customers actually value 'real' polish and not just a slick looking UI? If no, then real polish doesn't matter.

As a software writer you'll get your ass kicked into the ground by another company that writes catchy features and nice looking interfaces 9 times out of 10. So few actual customers know out to measure 'polish' that it's almost a non consideration.

Unless that polish has value. Thats the hard part, knowing what features to really spend that extra time on, and which to 1 and done.