I understand these are sample projects and are not representative - but a couple of quick comments:
Do not put tasks in your resource pool file.
When viewing the pool file "Test Project One" and looking at the Resource Usage view, I see % Allocations on the Resource line without problem. I'm not sure why you were not seeing this information before. The % Allocation shows where there are assignments, so click on the Resource's name and then use the Scroll to Task button on the Task tab to quickly view the assignments for the selected resource. If you zoom out to show weekly or monthly, this may also help with the % data you were seeking. Bear in mind that % Allocation is % of Max units. So if you have resources at 100% max units it's pretty straight forward. If you have them at 50% max -- and % Allocation shows 100% - it means 100% of 50%.
To get the information that you are seeking, you're likely going to have to take the data out of Project as you cannot refer to different tasks or resources with custom fields.
To address each issue:
Resource time spent on a task compared to the whole project
Create a custom filter in the Resource Usage view to group first by Name and then group the assignments by Project. With the work field visible, this will show total work for the resource (on the Resource group), total work for Project (on the Project assignment line) and then each task in each project underneath. Add the Cost field to the Usage table and that should also give a cost comparison.
A task (estimating) compared to that task (estimating) in other projects.
To compare estimates against actuals you'll need to save a baseline to capture work, duration, and cost estimates. Then track actuals to get the comparison.
If you want to compare tasks across projects, again, a custom group will be needed grouping assignments in the Resource Usage view. The trick is going to be that the tasks have to have the same name in each project and I think that is a low probability unless you work with a standard template for the creation of all projects.
A project compared to other projects in its class (not defined here)
If you use a text field to hold "class" a custom group should show you that information.
A project compared to all projects.
Again, group the Resource Usage view by Name and then group the assignments by Project.
I hope this helps.
I also suggest investing in some good hands on training with MS Project. It is not an intuitive tool and using it correctly will aide greatly in reduction of aggravation and in the generation of meaningful accurate data for management.