Peninsula water is municipal and relatively soft, so the honest answer downtown is that most homes do not need a softener.
We will tell you when not to buy
If someone has quoted you a whole-house softening system for a downtown address, ask what hardness reading it is based on. Softening solves a problem the peninsula largely does not have. Summerville does; here it usually does not.
What people genuinely notice
Chlorine taste and odour, and discoloured water in older houses. The second is worth separating carefully — rusty water first thing in the morning generally means corroding galvanised pipe inside your own house. Filtration masks that; repiping fixes it.
Where filtration does help
Sediment filtration protects fixtures in homes with old supply lines, and a point-of-use drinking filter at the kitchen tap is a modest, sensible improvement most people are happy with.
Test before buying anything
Equipment recommended without a water test is being sold from a catalogue rather than fitted to your house.