I assume that the literal reference is to a mother spitting into a handkerchief in order to wipe some dirt from a child's face. Obviously, it's better to use water, but if there's no water, spit is better than nothing.

So, figuratively, it means not only a "minor renovation," but perhaps a "hardly sufficient renovation (that was just slightly better than nothing at all)".

I've never heard the specific phrase "licks and spits," but there's a similar phrase "to give a lick and a promise", as in "The boy gave his hair a lick and a promise." (Meaning: He used spit to smooth his hair down, and "promised" to comb it or wash it properly in the future.)

P.S. In US military slang, at least, "to spit-shine" (in reference to shoes/boots) actually means to give the footwear a very thorough, high-quality, professional-looking, mirror-like polish -- whereas "licks and spits" and "lick and a promise" imply a quick and superficial attempt to make something look better. So they're rather opposite.