Unless dampproofed or waterproofed, concrete won't stop water vapour movement. So that wouldn't be my worry.

However, bonding new concrete to existing concrete is quite the art. And when you're investing in stamped concrete, it would often be prudent to start afresh with a new pour.

If you're using ceramic tile, water vapour will move upward through the grouting. When I use ceramic tile on a basement slab, an uncoupling underlayment is a must.

Thanks for the information! So if I tile, i shouldn't have an increase in the musty smell because the water vapor will move through the grouting? The house works just fine as it is, I don't want to rock the boat and make a change that will start a mold/mildew problem. I'm looking to give the basement a more finished look that's very durable (bikes get stored in there, kids do "projects", etc. Tile will work fine for my purposes.

Water vapour will move upward through the grout if you don't use an uncoupling membrane, which is not a problem.

If you use an uncoupling membrane, they are typically water and vapour proof. The systems I've used are from Schluter, which originated the plastic membrane products in Europe.