Suggestions for managing a large parking lot?

I recently found WorkPlan, and really like a lot of the features and the layout. I'm trying to duplicate my existing task manager's organization in this tool, and I'm having some trouble organizing my parking lot in a way that will be usable going forward.

I have a lot of nested lists in my current tool's parking lot (9 main categories, plus an inbox), with about 50 sub lists. For example, a main list, Home, might have a bunch of sub-lists, for example 'Garage Rebuild', 'Gardening', 'House Cleanup', each of which has a bunch of tasks under it. Some of these are transient (e.g. projects) and some are permanent (e.g. Gardening) I tried laying all of this out in WorkPlan, and the parking lot becomes a disorganized mess very quickly, as there doesn't seem to be a way to organize the parking lot lists into groups (e.g. sort all the lists with a particular role together, or filter them on and off, so I only see the 'Home' related ones when planning out activities for that role). I could take the time to put them in in order, and use a naming convention (e.g. Home: Gardening) to be able to tell when I've moved from one section to the other, but that will be a pain to add new things to over time.

I was thinking instead that I could create a workspace for each major category I currently have, and set up my parking lots there. It seems that I could then have a much more structured approach, and by using the feature to see tasks across workspaces, I could still have a single view of scheduled tasks, but more organization for someday tasks. The issue I'm seeing with this approach (and I'm sure there are others) is that there doesn't seem to be a way to move tasks across workspaces, so I couldn't use the GTD single inbox approach, and then process the tasks into the right lists.

Another thought would be to use only my high level categories as parking lot lists, and then use either tags or tasks with subtasks to organize each list. Subtasks are hard to read at a glance. Tags could work - need to play with that more.

Any ideas? Thanks.