I agree, it's not worth it to go from 4.56's to 4.88's unless you're installing the gears yourself so there is no labor. The difference is around 2-300RPM which can make a difference but is pretty small unless you do not plan on going any larger ever.You will not recoupe any labor costs by selling the old gears which is usually half the cost.
Only reason I geared to 4.56's was because back then, 4.88's weren't on the market. I also installed them myself so the cost of changing gears was minimal ($408). I've thought about gearing lower but it's just not worth it. I'd rather gear to 5.38's and leave the front till I swap it out but by then I might just swap both axles out and start over.
I do know someone who went from 4.56's to 4.88's and liked the difference but the law of diminishing returns really rears it's ugly head.