I really don't see the need for wax on the plastic...the wax does absolutely nothing to protect against scratches. It is designed to be a barrier coat to protect paint from getting oxidized (that chalky look). Modern Basecoat/Clearcoat paint systems really don't need to be waxed like the older lacquer and enamel paints (which oxidize quickly when unprotected). Being the macbook is some sort of plastic, the wax is a waste of time.
Something you could do to "refresh" it would be to use a good automotive quality hand glaze or light polish to remove some swirl marks...."scratches" that can be felt with your fingernail, don't even waste your time rubbing, anything short of a buffer will not get those out (on plastic). I have buffed out plastic black mirrors to like new with a rotary buffer, foam pad, and a 3 stage compound system...nothing you want to try on your macbook
If you
have to wax your macbook, at least use a nice hard carnauba wax that wont melt as easily, and please oh please don't use turtle wax "ice" I would not even use that on an Ford Escort. If you do want to go the hand glaze/ polish route I would recommend 3M Imperial Hand Glaze or the smaller bottle of the Maguires equivalent...has to be bought at an automotive detailer shop or some kind of auto body supply store...works great and wont leave anything behind after your rub it off.
Just my $.02