Wats of Liberty - slaves and pioneers

So I played with WoL for the first time yesterday, with America, and it got me thinking that there's really no benefit to training slaves.

I mean, yeah, they cost gold instead of food, but it's the same amount of resources, just in gold - and the Dutch already have this.

Considering the time period, why not make slaves a little more appealing?

I would say, if you are playing Confederacy, make them cost something like 60 gold, and if you go Union; change them to "Freed slave" (or something like that), and make them be full price, but count for only 2/3rds of a regular settler.