I voted for the 'Creative' option. Porsche made racing history with cars that where very loosley based around the rules, such as the 935's. He who interprets the rules the best gains the biggest advantage, and I see no issue with that. All competetiors still theoretically have the same options available to them (based on resources of course), so I don;t think it's wrong to reward intelligence and ingenuity.
As for reliability modifications, unless it is previously agreed to or explicitly listed in the rule books (and cannot be creatively interpreted), then I don't think they should be automatically allowed. As Troy has said in racing reliability is a major factor, and thus can be a great advantage whether it affects outright pace or not.