This looks pretty smooth. Why cover it? If you don't like the look you can power wash it. If there are high or low pavers you can pry them out and re-level with brick sand and a rubber mallet.

The other advantage of pavers on a sand bed is that the water drains through them. On solid concrete you have to take care to slope the path slightly away from the house or you get standing water.

Putting concrete over that is not DIY in my opinion, and what you mentioned about a thin mix sound wrong. If the concrete is flowing there's too much water in it and the result will be weak concrete. I'm not a concrete contractor so that could be wrong, but the times I've used it the mix was like peanut butter and had to be shoveled, screeded and troweled in to place. Not easy.