With Ukraine we are already seeing RoI in terms of the amount of Russian equipment getting knocked out by US weapons, and the Night Vision stuff we sold Ukraine let's them operate at night, while the Russians have to pause at night because they have so few night optics.
I was doubtful about the legitimacy of this conflict before it began, because I still thought Putin was a rational actor. Now, after what we've seen the past couple months...this is a very righteous war and one where American's aid might do more than line the pockets of certain DC favored companies.
It also let's us bleed Russia of manpower and high end weapons (Russia's PGM stockpile is almost gone, which is why they've switched to using massed arty fires and not tactical CAS with smart weapons), has alienated Russia from most of the world, and has shown that Russia's conventional forces are a hollow remnant of the Soviet military. I mean, there serious questions about how much of Russia's nuke stockpile is actually in operational shape, and how many of their warheads have been properly serviced/refurbished since the end of the Cold War.
So no, I don't see Ukraine as another Vietnam, Iraq, of A-stan, when it comes to the US sending aid and weapons there.
My only real fear is that Putin truly is terminally ill with advanced Parkinson's, and may decide to go out in a 'blaze of glory' rather than be known as the leader who botched the Ukrainian invasion.