To be technical, you could still see an object that is smaller to than your resolving power (this happens essentially every time we observe individual stars). The issue is what is called the "confusion limit" - the point at which you can't be confident that what appears to be a source is not just the summed emission from a bunch of fainter background objects.

But you are right that increased resolution is key. The higher resolution helps you beat the confusion limit by working to resolve the faint background sources into individual objects, so you can separate them.

So, if you wanted to be certain that what you were seeing was the refracted light from Earth, you would need the high resolution to be sure that what you were seeing was actually that reflection, and not just a superposition of fainter background sources.

More on the confusion limit: http://coolwiki.ipac.caltech.edu/index.php/Confusion