Cake recipes are often quite finely balanced between flour, liquids, fat and sugar ratios, and if you change the recipe too much, you risk failure. I'm a keen home baker, but I have had my share of disasters when getting the ingredient ratios wrong. So, be warned - there is always a risk when experimenting!
However, I have found it is possible to reduce the sugar in a cake that uses the creamed butter-sugar method, but if you go too far it will adversely affect the texture of the cake. Perhaps start with a 10% reduction in sugar, maybe up to a 25% reduction, and see how it goes. Any less than that you will probably find the texture becomes denser, less moist, and more rubbery/chewy, and it might affect the rise. You could even get sinking in the middle.
Another thing to be aware of (I have found) is that cakes with too much vanilla often taste super sweet. For me, vanilla seems to intensify the sweet flavour, and can easily overpower a cake. So you might want to hold back on the vanilla.
Cake with salt as a replacement for sugar doesn't appeal to me.