Besides a quantum theory of gravity, etc, as mentioned by @JoWehler, consider the first half-or-so of the 1800's, where we had more-or-less separate theories of electricty and magnetism. That worked fine for inventing the telegraph and similar stuff, and maybe you might have thought "why would we want to unify them [electricty&magnetism]?"
But then Maxwell came along in the 1860's and did exactly that (adding a new "displacement current" equation to conserve charge). And then, voila, strange and wonderfgul things emerged that had never before been imagined. For example, by combining the equations for electricity and magnetism, an entirely new equation emerged, predicting the existence of electromagnetic waves. Moreover, it predicted the speed of those waves, sqrt(1/mu*epsilon), simply from measurable electronic properties of material (including the vacuum). And that turned out to be exactly the same as the already-measured speed of light, whereby light was finally understood to be an electromagnetic wave. That would never have happened without unifying electricity and magnetism, and we'd never have invented radio, television, etc.
Who knows what strange and wonderful new things will emerge from further unification? Quantum electrodynamics has already succeeded in unifying Maxwell's electromagnetic theory and quantum mechanics. And that's indeed revealed wonderful new insights, although nobody's invented a "stargate" or any such thing as an outgrowth of that. Not yet, anyway. And pretty much ditto for the standard model (aka quarks and such stuff), leaving gravity the only not-yet-unified fundamental force. Whether or not unifying them all opens the door to a vast new technological regime of astounding gadgets remains to be seen. But astounding new insights are an absolute certainty.