As the proprietor of one of the largest Award Booking Services, I wanted to say a few things. First, to OP's concerns:
For most awards, I need the following info: full legal names, gender, birthdays, account info and pin/pw. For AA awards, I don't even need account info, gender, or birthday.
Then I put an award on hold, and you book it with your own credit card. In some situations, it is not possible to put an award on hold. In those cases, you can choose between giving me the credit card info by phone, which I shred afterwards, or calling in to book the award yourself with step-by-step written instructions.
Now, to the value proposition:
At $149 for two passengers on one award, my price, almost everyone gets incredible value from a good award booking service.
First, it will save you tons of time. Any time you have to get into a phone call with the awfully-trained agents of a few airlines, you are staring at an hour. What do you value your time at?
Second, it will save you taxes and fees. My personal record is saving two people almost $2,000. In many cases, I will save $50 in phone fees by using phone-ticketing tricks.
Third, you can add free oneways and extra legs. You may know the rules for all airlines in this regard. We do.
Four, you will not have to think about which of your 5 types of miles/points is best for the job.
If you just want a domestic oneway on United, an award booking service would be a waste of your money. But if you want anything with any complexity, and you aren't a complete expert yourself, you will get good value.
Finally OP made another interesting point: "And, also considering most services operate blogs, isn't their service the exact opposite of what their blogs attempt to provide?"
The short answer is yes, which is very interesting for me to ponder. If you read and understood every post on my blog, you would basically have the same award-booking acumen I do. I am giving away for free what I charge for. I can't think of other businesses that do that.
Altruistic reason: the main purpose of milevalue.com is not profit.
Selfish reason: It turns out to be a successful strategy because it advertises my acumen and draws in more potential customers.