You may or may not notice an FPS increase, but with FSX (being 32-bit application) the main improvement will be less OOMs (Out Of Memory errors).
Other than that, if you're running your weather engine on a networked computer you will experience no FPS drop when the weather updates itself and gets injected to FSX.
I say it's definitely worth it for FSX. Maybe worth it as well for P3D, no matter what version. If you like to run a lot of addons like me then it's definitely worth it. Look up in youtube 'frooglesim' channel, that guy has a very easy step-by-step tutorial on how to connect FSX on a network. ;D