You're right, all of the contents of a RAM disk are lost after power down. If you put your computer to sleep, the contents would be kept, but eventually every system needs a reboot.
If you need the kind of performance a RAM disk offers, then you could go that route. Really though, they have limited application anymore. Windows is quite good at caching data as it sees fit, and it will do this the first time you load data into memory, which really is no different than loading up a RAM disk. The only difference is, on a RAM disk you have to put the data there, whereas with Windows, it happens automatically. Since you put the data you want on the RAM disk yourself, you have more control over when that happens, so in essence, you are really just pre-caching. However, you could drum up other uses for a RAM disk if you preferred, such as holding temporary files, or browser cache files, or things that are updated often instead of sending those to something with SSD like write characteristics.
Putting your swap file on a RAM disk, while it may sound like a good idea on the surface, is not.