wouldn't it be possible for the spaceship to be engineered to run on both rocket fuel and methane?
I don't know how far you'd have to go down into Urstar fish' atmosphere to find a decent concentration of methane, but the amount of energy you'd have to expend to escape the gravity well would be ridiculous. Consider also the fact that any methane you collect
adds mass which requires additional fuel to reach escape velocity. Basically, you'd need a ship bigger than anything humanity has ever built, and it would still burn up the vast majority of the fuel just getting out of the planet.
On the other hand, we have vast stores of methane sitting right under us which can be pumped up with far less waste.
Spending billions of dollars to build spacecraft and fuel for it to fly around and gather information is a waste of money. It'd be better spent actually building the new technologies like the list of things NASA built, not funding a useless mission that will sprout technologies as an accidental biproduct
That's the thing you're missing here. These technologies sprout as a byproduct of sending probes to do scientific research. If you aren't sending probes to do scientific research, then you aren't getting spin-off technologies. It's not a waste.