How do you determine if it pays to remodel a master bathroom?

[Phyllis E.]

How do you determine how much (if at all) master bathroom remodeling to do in order to make money on the investment?

Flippers and remodelers typically remodel the bathrooms in their rehabs, correct? Then how come those "costs vs value" charts typically show a bathroom remodel as averaging only 58-65% return on investment? (as shown on this chart: http://www.remodeling.hw.net/cost-vs-value/2016/middle-atlantic/) I know these are just averages, but they would have to be low by over 35% for anyone to make any money by remodeling the bathrooms, according to these figures! Just wondering if you all have any insight into this. Are those ROI charts way off? How dated or "broken" does a bathroom have to be before you should invest in improving it?

(Sorry about the large type and mixed up formatting---I can't figure out how to shrink it back to normal size and not sure how it got so big in the first place!)

Here is why I am asking: I am trying to fix up my own home, of 23 years, to sell it this summer and am trying to think about it as a  business investment or "flip". ( I would love to eventually try some house flipping, so I am sort of thinking about this like practice, LOL! ) I am trying to determine if it would pay to do a more major remodel of our master bathroom (The house was built in 1987, btw.)  The vanities were in bad shape, so we have already bought some upgraded vanities with real marble* tops and new faucets, but not sure if we should also do a major remodel to replace the dated 1980's floor and wall tile, "Roman" whirlpool tub ("bone" colored), "bone" colored toilet, and acrylic shower stall. The current layout is  very awkward and is a poor use of space, but could be tremendously improved by just swapping the tub and shower locations/orientations, which I imagine would drive potential costs up a lot. We had several realtors through the house to give us some pre-sale, fix-up suggestions, and one realtor thought we should also replace the floor tile, along with the vanities, but, without improving the other things, I'm afraid it would be just throwing good money after bad.  So how do you determine when, and how much, master bathroom remodeling to do in order to make money?

(Btw, fwiw, I do have an architecture background from years ago (back before kids) and have already managed about 5 various home improvement projects on my own home here over the years!)

( * Just FYI, Home Depot now has real marble vanity tops in stock for unbelievably great prices--not carrara, but a type of marble called Arabescato Venato, which has both gray and beige and/or brown veining, so it can work with older beige and almond/bone colored tile, (like mine) too! If you buy one, though, make sure to take off the top and check it out before you take it home--being natural, the veining patterns vary considerably from box to box! HTH someone! )