There was another thing I wanted to add to this thread which I found interesting, regarding Paul's discourse on Christ's Resurrection and any possible pagan motifs he could have drawn upon as an aid.
It has to do with the Feast of First Fruits which is one of the seven great yearly feasts mentioned in Leviticus 23, and seeing Jesus as the fulfillment or embodiment of these seven feasts. The first feast is the Passover, on 14th of Nisan (Lev 23:5) when the Passover lamb is offered, and Paul had already referred to Christ as our Passover lamb (1Cor 5:7). The second feast is Unleavened Bread, and it begins on the 15th Nisan (Lev 23:6), where Jesus' body is referenced as unleavened bread (1Cor 11:24). Now, the third feast is the First Fruits which per Lev 23:11, occurs on the first Sunday after the feast of Unleavened Bread. Paul explicitly refers to Christ as our First Fruit twice in 1 Cor 15:20 and 23. Thus for Paul, Jesus' death, burial and resurrection were each "according to Scriptures" and corresponded to the 3 feasts of Passover, Unleavened Bread and First Fruits, both from a symbolic as well as a chronological view. (The other feasts of Pentecost, Trumpets, Atonement and Tabernacles) also fit in quite nicely, though the last 3 are at the 2nd coming.
The point of it all, is the Jews had their own holy feast dealing with fertility and seeds sprouting from the ground, and it goes back to the days of Moses, long before the Eleusinian Mysteries. I submit that if Paul had a fertility festival motif in mind as he presented Christ's resurrection, it was this Feast of First Fruits he had in mind, and not anything pagan. He tells us so himself "and that he was raised on the third day according to the scriptures" (1Cor 15:4) - only the Jewish Festival of First Fruit fits this "raised on the third day" motif.