i never met a mathematician who would claim mathematics is a closed system: indeed Gödel's Incompleteness theorem has two conclusions for logicians: 1) that there exist things which are not provable, and the implication 2) that there are things which are, but as yet undiscovered, thus guaranteeing employment for logicians and mathematicians, and yes, philosophers.
Certainly Philosophy is both a logical system and incomplete; to suggest Ms Rand's philosophy is one but not the either not only puts us all out of work but commits the Islam Messenger fallacy: that Muhammad is the final prophet and his message is complete unto itself, and he who questions divine authority must be expelled, banished even silenced.
You are right: new ideas that come about are philosophy ideas, theorems, theories consistent with Objectivism, logic and Reality: to equate Ms Rand's philosophy to a religious paradigm is not only dangerous, but hints at a deeper personal issue one may possess regarding the basis for knowledge and one's self worth.
To paraphrase Ms Rand, what we're talking about is not Objectivist philosophy, it's just philosophy, so get over it: it is imcomplete as any system must be, and to claim it is not Objectivism is to demean the system: Ms Rand is not a divine prophet, had a finite lifespan, and as Gödel showed, could not have come up with everything (indeed no one can) and like math, our theory will grow as does our comprehension; if you wish to close your mind, so be it: don't straitjacket the rest of us who can still wish to think.