That's a question with both philosophical and practical implications.

In all past eras of exploration, people entered new territories that were literally uncharted, territories nobody had ever seen before or even imagined...the great blank spots on the maps labelled "here be dragons". Our recently-developed ability to remotely sense a strange land before we visit may reduce some of the surprise and adrenaline, but being able to look before we leap means that exploration can be conducted more efficiently and quicker, and more safely. Space exploration is the most dangerous form of exploration we've ever attempted, and we need all the advantages we can get.

Philosophically...well, perhaps "Are humans necessary?" is a misleading way to phrase the question. Who sends the robots? Why do we send the robots? Without humans there'd be no exploration, so the question is moot in a real sense. Humans explore because that's what we do, and humans will go to the places the robots scout simply because we want to. We don't have to justify it to anybody.

Remote sensing also introduces two tiers of exploration that vastly broadens our opportunity to participate. A few will visit new worlds personally, while millions can explore vicarously/virtually through the cameras and the instruments. Perhaps sometime this century advances in materials and manufacturing will make personal robotic explorers inexpensive enough for individuals to own them and send them around the Solar System where their fancy takes them. An old science fiction staple is the grizzled independent "Belt prospector"; well, maybe it'll turn out that Belt prospectors stay on Earth and send their robots to locate resources in the asteroid belt, whose location they sell to the big outfits with the mining robots.

I think robots will make the future turn out differently than most of us have imagined, inspired as we were by science fiction tales of individual heroic personal exploration. But they don't foreclose a future of exploration. The best is yet to come.