Well, Gray, couple of things. Demons cannot replicate Transubstantiation, because some things, like Creation ex nihilo, or Transubstantiation, is above the power of demons. Only God Himself can create from nothing. Only God Himself can change one substance into another, and cause the first substance to cease to exist, as is the case in Transubstantiation. When the Bread is changed into the Body, or the Wine into the Blood, and that visibly as in Eucharistic Miracles, the mere bread or the mere wine, in substance, ceases to exist. The demons can't do this, so I don't believe this is demonic. What would be the point anyway? Millions of Catholics are confirmed, encouraged, strengthened in their Faith through such miracles. You really think God allowed it just so Satan could trick a few sedes who believe the new rites are invaid? I doubt it. Anyway, regarding the second point, demons themselves are untrustworthy, sure, but demons can be compelled by God to speak the Truth. We have at least two clear proofs of this, from Sacred Scripture and Sacred Tradition, respectively. (1) In Sacred Scripture, the demons are compelled to confess the Truth that Jesus Christ is the Son of God, the Holy One. (2) In Sacred Tradition, the demons are compelled by Our Lady, the Rosary and Saint Dominic, to confess the Power of Mary's Intercession among the Saints.
I don't disagree witth your words. Now let's take each miracle you are talking about and make sure we can prove it was actually a miracle. Pick your favorite and let's start there.
Why would God allow fake miracles to encourage people to stay sort of Catholic? My answer is because He doesn't want them to despair and become pagans or atheists.