I've always said my sons were really creative. They can make a mess with anything. Told you so.
Then the kind people at Meccano sent us some of their Space Chaos range to have a go at. At first I thought they wouldn't be captivating enough, but they can be dismantled and turned into a different kind of interstellar fighting vehicle. The boys love them and so do I - the bits don't hurt half as much as Lego when you stand on them.
Disclosure: we were sent Meccano Space Chaos sets to try.