I agree at some point with you Eddy.
The boss battle thing is kind of ....well....not so great...
But the building contest is a good idea.
However, let's elaborate on the building contest, I do not think it should be limited to Castles/Houses/ete. Only because some people are not so great at that, however, who ever makes the best construct with limited supplies, could win.
Let's say they both start with four stacks of stone, three stacks of wood, some wire, cutters, wrench, axe, hammer, pickaxe, two stacks of sand, and some miscellaneous items.
Set them loose, and see who makes the better construct with the equal amount of items.