There are marketplaces for speakers: espeakers.com, orate.me, bigspeak.com, kepplerspeakers.com, speakermatch.com, eaglestalent.com, celebrityspeakersbureau.com, among others. The speaker profiles include prices, areas of expertise, and a way to inquire and book. What they don't show, that you're asking for, is speaker availability and popularity. The problems I see with disclosing the schedules of speakers: 1) celebrities have real privacy concerns, 2) talent does not want their real demand every day of the year exposed to the public because it can hurt the mystery of their appeal, and 3) disparate calendaring methods maintained by each speaker mean that no web site can be in sync with all of its talent thus instant online booking is hard to do. As for the popularity requirement you asked for ("well-regarded") this is difficult to define because assessments are nonstandard; so what you get in all speaker marketplaces is endorsements and accolades the speaker cites themselves in their own profile -- which will always be self-recommending.
No, none of the sites you mentioned solve the problem I posed.
Bigspeak, Keppler, Eagles Talent, and Celebrity are bureaus and function in a traditional way. Espeakers and SpeakerMatch are essentially speaker directories -- they make money from speaker's paying them a monthly fee or in a lead gen style.
Orate.me is new to me, I haven't seen it before. In a cursory look at their site, it looks like their speaker list is just NSA members.
Also the calendaring problem is easy to solve...
There's enough public data to develop a sentiment algorithm and solve the popularity problem.
When I worked at a bureau, we had a running joke... When a meeting planner asked, "How much is so-and-so speaker?" We'd reply, "What's your budget?" Coincidentally, that was how much the speaker was. Regardless of how much we knew the "rack rate" of that speaker was.
During the 2008 election, Rudy Giuliani was running as a Republican nominee. When his financial disclosures came out, he surprised everyone with how much he made on the speaking circuit. News orgs filed FOIA requests to see what universities and public institutions paid him to speak.
For some events, he'd speak in the same city to different groups. The price each group paid was wildly different (+/- 50k). The meeting planners hit the roof.
Speakers bureaus do not view meeting planners as their clients, the speakers are.
