I have a simple mod if anybody is interested:
http://steamcommunity.com/sharedfiles/filedetails/?id=173971334
And also an alternate version if you prefer different yields:
http://steamcommunity.com/sharedfiles/filedetails/?id=175409871
I believe the default game's salt is a bit too much as well. Getting 2 bonus yields from improving a tile is a lot early in the game; especially when the bonus is extra food and production. When it becomes a regional luxury within a game, it can cluster very easily for a civ which makes all that extra food and production even more powerful since they're "local" yield types which greatly affect the city they're near, instead of other yields which are more global, like gold or culture.
Also, it doesn't only come on bad tiles. In fact, flat plains are its primary choice of terrain (and I wouldn't call plains bad), followed by flat desert, then flat tundra (with or without a forest), and then finally any tiles with forests (so that means it can be found on grass too).
I could certainly be wrong, but I believe the yield total for salt was a bit of an oversight during development. In the code, there are two ways an improved resource receives its bonus yield: either it's tied to the improvement or it's tied to the resource.
Improvements like mines and farms are not only built on resources, but normal tiles too, so their bonus is tied to the improvement itself. Other improvements like plantations or fishing boats are always built on resources, so their bonus is tied to the resource type. Salt receives both of them: 1 production from the mine itself and 1 food for improving the salt resource.
The mod above removes the +1 production from the mine and gives it only a bonus of +1 food when improved, so it totals 2F1G when improved (similar to crab).
The alternate mod changes the +1 food to +1 production with the mine instead, for a total of 1F1P1G, if you prefer more consistency with your mine improvements. Though, keep in mind, other improvements already have inconsistencies, such as pastures which give +1F to sheep and cattle, but +1P to horses, for example.