I agree with many things you all say in here, but I would like to add something. In many cases the reboots are made to fit with a new generation of viewers, a younger generation who preffer more action, more special effects and more blood. Many of those viewers have heard of the old movies (or not) and they see them as something made in the past (the past is not cool for many). So they make reboots of old films and TV series like The Planet of the Apes (which I didn't like the new ending), Starsky & Hutch, Charlie's Angels and others (Star Trek among them). While the ones who remember and loved the old ones (I'm 40yo, by the way) are a public that go less to the cinema (family, work, no work+no money...) there many new people who can afford going to the cinema every weekend, and these reboots are made for them. I'm not defending that, money is money.
Now, reboots like Batman or Spiderman, with cool special effects, just better in the reboots, if the reason is to tie them with more advanced movies (already done or upcoming) I don't understand why they don't simply continue with new stories. They could still do that with better special effects, no need to reboot them.
If the reason is that the new director, or producers, or whoever think that they can just do it better, well, they could prove that with a new script, a new series.