Upgrades

Info about the other two games (Scrap Clicker and ScrapTD) is missing.

Upgrades are important in every Scrap games to progress anywhere, they are the main source to focus on when first playing the game.

With the Tree Upgrades
Tree Upgrades are unlocked at x40 Stars. For the complete list refer to the link in the title.

With Tires
NOTE: The formula for the costs is irregular. Also each of them goes at different increase speeds.

In Scrap Collector
Here's a list of Upgrades found in Scrap Collector, with Scrap and Magnets.