it does mean i miss you, that is how it is used, the literal translation being you cause a "lack" in me, as in some part missing, it's not neccesarily "you" but more the fact that you are gone, though the sintaxis does not reflect this, it is an easier way to understand for an english speaker. me falta= i lack, ie i lack milk, i lack a car, used as(or in other words we say) "i don't have" me haces falta, hacer=to make, haces=you make me haces=you make me[somthing](though used differently, not make)
can also be thought of as "you make me lack" since the "hole" in me, is caused by your absence. though it is not putting any degree of "blame" on the other person.
"si un dia me faltas" is more like "if one day you leave me" (as in are gone) but also can be used to tie in that idea of missing you. but i believe that hacer falta is more direct and appropriate. [as used in man on fires closing song, una palabra, by carlos varela, "si un dia me faltas no sere nada" if one day you leave me, (or are gone, ect...) i will be nothing
any opinions? this is an interesting question, i'll have to hit up the davies spanish corpus and see what i can find.