I think using WCF provides a robust solution to the need for executing SSIS packages remotely. I also think there is value in using Broker Servers when the resources for developing a WCF application are not available. The solution depends on the environment and resources available.

Agreed, passing a variable collection as you are doing is more attractive than having to build up a dtexec string that a stored procedure requires.

In regards to handling errors and getting error messages back from an SSIS package, I think WCF and Broker services offer similar functionality with a difference in implementation. Starting up a conversation to send a broker message to start a package does not mean that the conversation has to be over.

I use broker services to execute SSIS packages, and I also include broker messaging in my SSIS error handling where called for. If a task fails, then I can add an error handler to the task which calls a stored procedure to send broker messages back to the application. So a DBA can implement messaging with the skill set s/he already posses. This is where Broker Services shines in my opinion.