Yes, lower launch costs have enabled a lot of missions and cheaper spacecraft than would have been possible otherwise. But space is still hard. There is also an element of the fallacy where if there is more resources available the expectation is cost will go down, but the response ends up people just use more of the resources (there is some economics fallacy/paradox term for this that escapes me right now). Larger launch vehicles enable larger more complex spacecraft. I expect that the capability of the Falcon heavy means that the size of the Uranus spacecraft will be much larger and more complex than something like Voyager 1/2 or New Horizons.