I would have to say that this is indeed a good idea for development environment. We have been implementing this on our dev environment. I have to agree with Brian that the problem with this is, of course, keeping the permissions up-to-date. And I would like to share our own way of dealing with this. We have also created a SQL Server Agent for the script that grants permission on all stored procedure to a particular role but as a DBA, i didn't assign a schedule for it to run, instead, I created an alert for that when triggered, will then trigger the SQL Server Agent that runs the script. So when a developer creates or drop&re-create a stored procedure, all he has to do is to execute a raiserror to trigger the SQL Server Agent that grants execute permission on all stored procedure for that particular role.
I hope I was able to share something worthwhile.