Reducing the first press of the macerated raspberry mixture before adding the rest intensifies the raspberry flavor. Kiwis are naturally very high in pectin--just one will thicken the preserves nicely.
Combine sugar, salt, and raspberries in a medium bowl. Scrape seeds from vanilla bean; add seeds and bean to raspberry mixture. Cover and let stand at room temperature at least 2 hours or overnight.
Place raspberry mixture in a fine sieve over a bowl. Press on solids with a spatula to extract liquid; reserve solids. Place raspberry liquid in a heavy-bottomed medium saucepan; bring to a boil over medium-high heat. Cook 6 minutes, stirring frequently. Add reserved solids and any remaining liquid to pan. Bring to a boil, stirring frequently. Add kiwi; reduce heat to medium-low, and cook, stirring occasionally, 20 minutes or until mixture has thickened and bubbles pop slowly on the surface. Remove pan from heat; cool 5 minutes. Discard bean. Stir in butter until melted. Cool completely. Place in an airtight container; refrigerate up to 2 weeks.