I am about to install laminate flooring tomorrow in our investment property house. I was wondering since I have scraped the nasty tile off the floor and only concrete slab remains should I lay down a thin plywood? I have the underlayment, but I always tend to do things with the utmost care which is why I ask would plywood be a good idea under the underlayment?

Here's what I would do;

Lay a 6 mil poly vapor barrier on the slab. Install pressure treated 1x4 sleepers, 16" on center. Put 3/4" styrofoam between the sleepers. Underlayment attached to the sleepers. You can shim the sleepers to account for any grade differences in the slab. You should never allow any non pressure treated wood to come in contact with masonry. I hope this helps.