I received my Kickstarter copy of Florenza today (the publisher managed to mess up my address on the parcel which didn't help!), and it of course included the Kickstarter bonuses. The one item that has an effect on the gameplay (i.e. isn't just an extra dice or meeple) is the 'La Musa' card.
On the game's KS pages, this is said about the card:
"MUSA card. This one allows the user to re-roll the die while determining the artwork value of an artist at cost of 50 florins."
I presume that, similar to the rule about artworks in the Cathedral (page 12) one rolls two dice and chooses the preferred result when electing to use (and pay for, obviously) the Muse.
Rulebook p12 wrote:
Important: If the artwork is in the Cathedral, roll the die twice and choose which result to use.
So, if one were to use/pay for the ability of the Muse in the Cathedral, I would assume one could roll one extra dice (a total of three) and then choose the most favourable.
However, I would like to see some official response from Stefano et al, as to whether this is the correct interpretation.