I guess it comes down to your own personal preference. Obviously you prefer "pick up and play" games.
I don't see a need to put these two kinds of games up against each other. All games serve their purposes and I'm glad that they all exist. Choice is good.
I'm not feeling the terms 'board game' and 'workshop' to describe music games. 'Pick up and play' might work for games that are easy to quickly start playing without the need of preparations, set up, and / or practice. Maybe some time to learn the rules. Though, they might include props, such as cue-cards or dice, as they can be readily available and don't require any extra time.
I don't understand where the term 'workshop' came from. I might need more information about that term. I can't think of any game that would be restricted to a workshop setting.
1. Preparation - I don't know any games that require all players to prepare props ahead of time. If some kind of preparation is required then it's usually one or two people who do it, usually those who set up and are in charge of the game meeting. Unless it's a classroom setting and an assignment is given. Usually these preparations are small - such as "come up with a motif," or "think of a few events." Big preparations are almost always done by the people in charge of a game meeting. I often the one who's in charge of game meetings so I might have to build, for example, a wooden spinning wheel for a game. I'm one of those people who would gladly do it! Then I have a spinning wheel in storage for whenever I need it for future games! At most of my game meetings, gatherings, workshops, parties everyone shows up with no extra preparations needed. Except if they're playing they might have to bring their instruments.
"the ideal situation is to provide a ready prop and encourage players to make their own versions (if they will)." I agree with this.
2) Not specifying all rules - For the most part I agree. Game rules contributed to this wiki library should be concrete, unless there is a specific reason to have free choice in the mechanics, I still imagine it would be rare. There is also a Variant chapter that can help solve some problems that might arise in being strict with this rule.
However, there are times when not specifying all the rules and leaving choice is important. Creative education for example - which would include classrooms, workshops, videos, or whenever one hopes to get people to play 'game designer.' When doing this there should be an objective in place. What is the main idea to be taught? And that objective should be the core of the game mechanic. We might even want to have an 'educational games' category here in the future, but for now, the library is for people to find games that they can play. So, for the most part, the game rules should be complete. If a mechanic is left open, most of the time it's just bad game design.