Salt by itself is not really a culprit of weight gain (at least, not in the way that sugar is). However, as you said, it does cause water retention. And this CAN affect your weight long-term.
I've been chronically under-hydrated for years, and only recently have I stopped drinking diet sodas (which contain sodium) and completely switched over to water and milk only. I've already lost 2 lbs of water in 3 weeks just by drinking MORE water. It's counter-intuitive, but true.
ALSO--being dehydrated keeps your kidneys and liver from working properly. The liver ends up doing the work of your kidneys instead of metabolizing fat, which is the job it's supposed to do. So maintaining proper hydration can increase your body's fat-burning abilities.
If you eat a lot of salt, just make sure you're getting lots of water (and watch that blood pressure too).
(HW = 153)
(CW = 127)
(GW = 118)
Hanging in there for the last 10