The more I think and read about the spiral/viral concept, the more I’m convinced that they actually need major re-design of a curriculum to work.  In fact, significant shift in the forms of teaching learning and assessment require not only teaching events to be re-designed (‘constructive alignment’), but the student timetable needs considerable re-design as well.   This also fits with other research that has investigated the effect of collaborative use of ‘authentic task’ materials.  In an experimental / control group experiment on use of such materials, for instance, Vermetten et al found evidence of improved performance in students only where the authentic approach was a prominent element of the curriculum.

Vermetten, Y.J., Vermunt, J.K., Lodewijks, H.G. (2002) Powerful learning environments?  How university students differ in their response to instructional measures.  Learning and Instruction, 12, 263-84.  See also Vermunt, J.D., Verloop, N. (1999) Congruence and friction between learning and teaching. Learning and Instruction, 9, 257-280