I am an Adobe employee, but I am not commenting from the perspective of Adobe and don't have the right to make any additional license on Adobe's behalf. However, I can read legalese.
There is no harm in reading the license or the spec. The specification license is a conditional patent license that provides a license to implementations that are compliant with the spec for those claims that Adobe owns that are necessarily infringed by implementing the spec. The conditions that are not licensed are listed in the license, but loosely summarized as implementations that attempt to intercept or circumvent DRM-protected content. You cannot lose any rights that you already have by accessing or reading the spec, since the license only gives you permission to do some things that otherwise might be forbidden due to Adobe's patents (I do not know which ones, nor do I know when they might expire, but in any case you won't need the license at all if no valid patents remain or if you don't happen to implement the spec).
In other words, this is similar to the reciprocal patent clause that you will find in the Apache License except it is only given to compliant implementations (like the Java licenses), the only contributor in this case is Adobe, and it is only a patent license. The copyright license for the spec is very restrictive, but that would not impact your implementation unless you wanted to include the spec itself. (A protocol is entirely operative by nature and hence not itself copyrightable, IIRC.)
The spec document has the same patent license on the first three pages and then a long plain-text document in PDF that appears to have been formatted like an Internet RFC but not submitted as one (i.e., this is an ugly spec, but folks who are familiar with IETF protocols will find it natural aside from the fact it is copyright Adobe).
I have no comment on the protocol quality – never tried implementing it myself.