But it's because I store my boat inside. And I do that because it's more convenient for working on the boat. It helps that the mast is deck stepped, so stepping and unstepping is relatively easy.

The boat (a Rival 32) was in salt water all its life until I bought it (1978-2006) and is now in fresh water (Great Lakes). The only serious effect that salt water seemed to have is on the mast. Taking the mast down each year has given me the chance to inspect and work on the mast and rigging (rewired the mast, added a Solent stay, replaced halyard sheaves, tackled corrosion). Can't say whether storing with the mast down is better, however. Most boats at my marina are stored with the mast up year after year and don't have any problems. The main complaint I've heard is from my rigger -- people who leave their mast up tend to neglect to check their rigging and mast hardware regularly, which means when a problem occurs it's more difficult for him to deal with.