Phil, I disagree with almost everything you just posted, though some of the disagreements are admittedly on minor points.
Bonfires at Lúnasa ? I've heard of bonfires at Samain and Bealtine, but not at Lúnasa. Maybe there were, but I can't remember hearing reliable reports about them anywhere.
The bonfire customs were not secret. How, in a world with no electric light, to you hide a bonfire ? The bonfire-sports were carried on by Christians, not pagans, though they might have originated in pagan times.
There was no such place as "England" when Constantine was Emperor, unless it was in Germany. It was the Roman province of Britannia. This is picky, I know, but I at least find I get a clearer view of the past if I avoid anachronistic geographical references when possible.
The Saturnalia occur, or at least begin, on December 17, I vaguely recall. December 25 was bruma, "midwinter". It seems to be true, though, that Christmas was placed there partly because of a deep-rooted, ancient tradition of midwinter festivity of which the Saturnalia were a part. But so what ? Did Saturn continue to be worshipped with the same processions and sacrifices as before ? Everything we know about this holiday shows that it became a Christian holiday. Saturn was forgotten except as a literary reference.
The "thin veil" at Samhain seems originally to have been, not between living and dead, but between the workaday world and the otherworld of the fairies. It was Christianity which added a commemoration of the dead to the day.
Pagans did not "get really quiet when the church took over" Into the 5th century pagans and Manichaeans engaged Christians and Jews in debate. Some of the literature survives. Augustine's famous City of God is part of that debate (though written with other intentions as well) as well as his Contra Faustum (I may not remember the title right). On the pagan side I belive we still posess the writings of an author named Symmachus. The Platonic Academy lasted until Justinian's time.
We know of the goddess Eostre only from Bede. The name suggests a dawn-goddess. I don't remember anything about hares.
Samhain cannot reliably be demonstrated to have been "New Year to the Celts". It was the beginning of winter for the Irish. It may have been a new year for the Irish as well, though (as I mentioned in an earlier post) I don't know of any medieval Irish author who begins the year on that day.
The idea that self-conscious paganism has persisted in secret comes from Margaret Murray's now-discredited theory about the 17th-century witch-hunts. We have from the past reports (sometimes true) of Jews outwardly conforming to Islam or to Christianity while secretly practising Judaism. The "secret", in other words, was not always very well kept. But did the Platonic Academy move to Lithuania, the last European country to convert to Christianity ? Where then is its literature ? Did any farmer in the 19th century ever sacrifice a pig, a lamb, and a calf to "father Mars" in accordance with a custom he had learned from his father, who learned it from his father before him, and so on back to ancient times ? You must provide plausible evidence not only for the sacrifice, but for the chain of transmission. Was the perpetual fire of Vesta kept up ? Were the nuns of Kildare Vestal Virgins in secret, deliberately decieving their bishop while continuing the very same ancient rites of Vesta and the Bona Dea that Cicero wrote about ? Everything we know about these women is consistent with the view that they were sincere Christians, not cunning pagan decievers.