Well, there is artificial saliva on the market. It is intended for people with certain medical conditions and drug reactions that cause dry mouth. Kind of pricey, though.
Just for procrastination I looked up formulas for this stuff and xanthan gum, sorbitol, methylparaben, sodium carboxymethylcellulose, and various salts show up.
I also found some similar stuff called "lubogel-V", which is used for, um, medical examinations. $4.69 for an 8-ounce bottle.
Seems like you could hit the internets, buy a few food-grade ingredients, and whip up your own almost-spit-lube. Print up some labels and sell it to the masses.
To answer your question more directly, what I've found is that sugary drinks tend to make my spit "spittier."