User blog comment:Azelfland/Car dialogues: R&D completion and mastery challenges/@comment-31544835-20170707061007/@comment-32459272-20170707071427

glad you liked it. :)

now, about the storage space rewards, if you got every single previous mastery rewards -all the decals, the Chevy Camaro Z/28, the Datsun 270 Z, the 1965 Shelby Cobra and "the boat", which is the Cadillac 16 Concept-, the rest of the mastery rewards are storage expansions, which are useful if you want to get more cards for pro tuning your cars. i hope my advice helps.:)