Charlemagne's Palatine Chapel is beautiful, I love the pictures you included. I think this is an important chapel not only because it is "one of the most impressive and historic ancient buildings of the Carolingian Renaissance" but also because it is a living testament to the significant work of Charlemagne. It tells the history of his dedication to the arts, religion and education. It will help future generation realize the lack of these types of cultures to "middle class" citizens and how Charlemagne wanted to improve the standards. The relics, mosaics and other architectural features are important to preserve as well. They give us insight into the meaning of religion and the progression of style within the era. I think the symbolism of the three tiers is interesting. The fact that the dome represents heaven and the bottom tier earth shows the depth and value of both to the Carolingian period. 
What do you think is the most significant part of the chapel? The fact it was a center for learning, art , and religion commissioned by Charlemagne, the architecture and architectural features, or the relics, mosaics, stained glass etc?