They don’t need it - but you can upgrade them if. you want to spend money.

It depends on how you define "upgrade". If you mean wholesale replacement that could make a small or huge difference depending on choice and if fine tuned or not. Fine setup matters and varies with string choice.

My understanding is most Revstars come with bone nuts and thankfully the string angle from nut to tuners isn't ridiculous BUT different gauges and string types will be more or less "slippery" as opposed to "creaky" (lots of friction at the nut) due to materials and nut slot width and angle. The material, if bone, is OK (I actually prefer Delrin) but the depth, width and angle needs to suit the strings you use. It can also help to apply some lube like graphite (even from pencil lead) to the slots to minimize friction especially if you're a "bender".