I've been thinking that it would be a good idea to add an all minigames category that is lengthier than any%, but not as challenging as 100%. It would consist of just unlocking and playing each of the minigames once on a fresh save. I'm also thinking that the 100% run should also include the requirement of getting all of the character coins, since that category looks for full completion.

It doesn't sound longer to me. 100% requires you to get the Daffy head on all minigames (completing all 10 levels of each minigame without losing a turn), while a potential All Minigames run only requires you to unlock all the minigames. It is worth noting that some minigames such as Dodge and Splat Daffy don't need to be played to be unlocked, even though that minigame requires all of the character coins in order to be displayed on the Gag Menu. Essentially, the All Minigames run would be a little shorter than 100%, since less minigames would actually need to be completed.