@Kevin1165 Yes, an inquiry only requires a response. I have pre-approved inquiries as long as the communication from the guest has been such that I feel fine about them. Pre-approving an inquiry shouldn't block your calendar, it just makes it easier for the guest to go on to actually book, and easier for you as a host in that they then don't have to send a request for you to accept if they are indeed serious about booking (which you are correct, most inquirers aren't).
Even if you pre-approve an inquiry, if a request comes through before the inquirer has booked, if you accept the request, that will override the pre-approved inquiry. Inn other words, first to pay gets the booking dates.
What you should never do is waste declines on inquiries, as declines lower your acceptance rate.