They were done very much like the Rankin/Bass Christmas specials of the same era and my kids (8 and 4) love them. I don't think kids necessarily need high-tech production values to hold their interest. All you really need is a compelling story with characters that they can relate to.
"The Thunderbirds" is also making a comeback on Tech-TV, also similarly low-tech. That one probably won't do as well with kids since it is on a channel not really known for children's programming.