Can I play Salvage and not kill any Gear if I don't want to and just draw the card?

Yes, you can play Salvage and choose not to kill any gear, still drawing the card.

According to the card's text, "You may kill up to one gear. Draw 1," and Rule 352.13:

"If a card specifies that a player chooses “any number” or “up to” some number of Game Objects to be affected, they may choose any number of available targets, including zero. If they choose zero, the spell or ability can be played without any targets."

Because the card uses the "up to one" phrasing, choosing zero gears is a valid choice during the targeting step. This allows you to play the spell solely for the "Draw 1" effect, even if there are no gears on the board or if you simply prefer not to destroy any of your own.