You can see Gumption as a somewhat reverse Unexpected Courage. While UC increases your value by 2, Gumption decreases your goal by 2. Either way, you're two number better than you were before comitting the skill card. They both also have the same limit of 1 per test and are both innate (Which matters for cards like True Survivor).
So the question becomes "Why do I spend two experience to upgrade my two UC into Gumptions?" I decided to list some of the pros and cons.
Cons: -The 2 experience price (While small, it does matter for small xp campaigns where your XP needs to go to your core cards, and gumption is probably not gonna be ur engine unless you're playing a Darrel 0 skill test archetype).
-Has no icons. Therefore does not work with cards like Grimsly Totem or interactions that need you to discard card with specific items/quantity of icons (Minh's The King in Yellow.)
-Does not interact with scrounge for supplies, I guess.
-If you're doing a 2 skill test, you can reduce the test to 0. It then becomes an auto-win unless you draw your auto-fail token. On the other hand, 2 skill tests are usually easy enough to pass with. Which brings us to...
-Old Key Ring (Lv 3). Together with Gumption means you can reduce a 4 shroud location to 0. This is much more interesting as a 4 shroud can be difficult for most non-seeker characters.
-Combos with Shed a Light and Exploit Weakness. Although it's not the only way to achieve a 0 skill test (Map the Area, Expose Weakness, Breach the Door, Makeshift Trap) it's probably the most versatile. When you buy gumption, this is probably the deck you're running. And it's not like you can only use ONE of these methods to reduce a test value. Use them all to get to that sweet 0 when you're running 2+ tests.
-Combos with Darrell Simmons for the above reason.
-Weirdly, Combos with Grizzled if it has the "Nemesis" upgrade.
-Combos with Resourceful, if that matters to you.
Of course, you CAN run both copies of UC and both copies of Gumption. You can even put one of each in a test for that sweet +4 in whatever ya need.