I've got a KALA KA-ASMTE-C that comes with Synthetic nut and saddle! How much and what kind of a difference will it make is I switch them out for the tusq or nubone? Or should I just remain with the stocked nut and saddle?
Because it is an all-solid instrument, changing the saddle (and to a lesser extent the nut) will make a difference. The difference is noticable to the ears, but difficult to describe in words. I'll have a go.
The two materials you mention are basically hard plastics and will make some difference. However, I don't think is would be worth the expense and bother. I have had a Collings guitar for 15 years which has a plastic saddle of some sort (nubone, I think), and I have never bothered to change it for bone.
However, real bone will usually give a clearer, more distinct sound than plastic. Ivory is very hard and will transmit the vibrations very well, giving a very distinct, bell-like sound.
Metal saddles usually sound horrible (at least on guitars) as they make the note sound metalic and strident.
Hard wood saddles are interesting as they impart a soft, mellow tone. But they can make the notes sound a bit muffled.
I have 9 ukuleles and I have not bothered changing the saddle (and certainly not the nut) on any of them. I did change the saddle on a tenor Bruko to jacaranda wood, but I have since sold that ukulele. Often a manufacturer chooses a material for the saddle that sounds good. If plastic sounds good, why change it?
KEN