No offense dave - I just thought you may have had some experience with the sanding advice you gave. You know like what worked good for you and so forth? Nevermind
Let's start over, then.
The last think that needed dehorning was a sub2000 from Kel Tec, I ended up using the back of a knife to soften edges and some extremely fine sandpaper to soften the checkering. I got a bit overly aggressive removing some molding flash on the fore-end, I got frustrated and shaved off the annoying edge where the halves meet. That's the only spot you can tell I did anything, otherwise a wipedown made all my tool marks go away.
Prior to that I did some reduction on MrsBFD's Taurus PT111, it showed a bit, but just as a grey area on a black frame ... nothing that an application of dye or some honest wear wouldn't hide. It made a difference in her opinion of the gun for range time, and when she decided to trade up to an XD the recipient of the gun didn't have any complaints about the modification.
If you wanted to reduce checkering on something the best way to ID the problem spots is to shoot it and see where it is rough, then
cautiously round edges a bit at a time. Remember that the checkering is there for you to utilize in a panic with sweaty (bloody?) hands, not for comfort at the range. You'll have to determine your own compromise point, based on the actual defensive role of the weapon compared to the time it spends as a range toy.
Adding a grip sleeve makes the gun bigger, which may not be a winning option for a concealment gun.
Adding rubber may make a gun a better range toy, but will it help with a wet hand? Go try it out, take a water-soaked cloth and an oil-soaked cloth to the range and see if your inner tube helps you grip that compared to checkering ... I suspect that it won't unless you're using the handle materials used on kitchen tools or something.
But the best option for making your defensive guns ergonomic is to
buy a gun that fits your hand in the first place, closely followed by
accept that a handgun is a compromise. Not every defensive gun makes a great range toy, not every ultra-comfortable customized match gun has any utility for defense.
If the gun fits, buy it, make it work for you, and don't worry about looks or resale value.