Like, let's assume they made materia 30 spoils, pegasus 50 spoils and then enabled us to purchase random i210 or i235 gear for 5 and 10 spoils respectively. I still don't think many people would participate in the diadem. However, if it was arranged so that a party of eight could nearly guarantee one materia each with the possibility of more per hour run, then I think it may see a bit more action, being the most effective way to gather materia Vs.

edit: especially if the spiritbond range gets altered so we can spiritbond the easily craftable i220 gear to convert that into more materia.