The Steam Gauge value of my account is waaaaaay more than I actually paid for my games!
You may have noticed that Steam Gauge only returns the Steam store price of a game, and not the amount you actually paid for it. This is because Valve does not allow access to your Steam transaction history as they do for your account profile and games.
However, Valve does provide a tool for viewing total spend on your account (it does not include payments to external storefronts for products that redeem on Steam):
To see a detailed breakdown of your account spending, visit https://store.steampowered.com/account/history.
You may view other types of data about your account that Steam stores here: https://help.steampowered.com/accountdata
What is "OldSpend" and "PWSpend"?
While "TotalSpend" represents all funds spent on the Steam Account, "OldSpend" represents the subset of that which was spent before Valve's 2015 implementation of "Limited User" account restrictions and "PWSpend" represents funds spent on "Perfect World Entertainment" apps in Steam.
Why does this page exist?
Since Steam now provides this natively, Steam Receipt is no longer maintained. If you're interested in the project code, you can find it here.