Hello Nate, and Welcome to WAGS!
Restoring Cast Iron Cookware will not cause any lose in value, but will in fact, increase the value of a piece.... IF DONE properly!
Check out our Cleaning and Restoration board for information and advice on Proper methods to restore your CI.
Your Wagner is not uncommon, and looks like it may have condition issues with some pitting(?) but will still make a nice user once restored. Blue book value is $25-$35 in excellent condition, so valuation decreases with condition issues.