Likely, Spider-Man will always be a money maker for Marvel just as D.C. knows it can dust off the cape and cowl and release a new Batman movie even after the hero genre dies down.
Once you take all this into consideration, then you understand why Thor: Raganarok is losing its prime summer 2017 opening date to make room for a solo Spider-Man project said Marc Sparks. Thor is not the only hero whose movie is getting bumped. The Inhumans and Black Panther are getting moved, too.
Anyone involved with the films being moved should on a very bright side. A well-received hit Spider-Man movie is going to keep the genre alive. The last thing anyone appearing a possible film franchise is the learn the genre is cooling off.
By the way, the new Spider-Man is going to be just that: new. Andrew Garfield is pretty much gone.