In most churches that I have visited which perform infant dedications it seems to me to be pretty much a dry type of baptism. In my own particular church, which technically does neither infant baptisms nor dedications, we had a family who came from a Lutheran background. After the birth of one of their daughters the husband called me one night and asked me to baptize the baby. I thought that to be an exceedingly odd request since I am not an ordained clergyman by any stretch of the imagination and I am personally opposed to baptizing babies.
The following Sunday my parents attended church with me. At the beginning of the service the proud parents strode up the aisle carrying their baby in a lovely baptismal gown. My mother asked me what was going on and I told her that it would be a dry baptism. THe officiant, an elder, read the baptismal liturgy from some book, excising the references to water, and the parents went away happy as, I assume, their relations were.
If, in fact, infant dedication is merely dedication, why is it only done once and that in public? It seems to me that it could be done privately and in more than one venue. I once attended a service in which the pastor, who had recently adopted a baby, went to great lengths to explain why he dedicated the child in his father's church and not in his own church. I saw no reason that the child couldn't have been dedicated in both, or more, for that matter.
The bottom line seems to me that infant dedication is hardly much more than a dry form of baptism. In many churches, such as the Presbyterian church I was raised in, infant baptism (with water) the purpose was to dedicate the infant to God by the parents and the congregation. The baptism did nothing spiritually for the infant.