
Welcome to Stamp Collecting Forum!
In response to your question, yes, there is a market for Christmas Seals and Easter Seals, which many choose to collect, as they are plentiful and relatively inexpensive to acquire.
As for value, most of the modern ones have minimal monetary value, but are still quite collectible. Most collectors of these things are more interested in the designs/varieties than the dollar value of the items.
Here's a previous thread that specifically discusses Easter Seals through the years:
https://goscf.com/t/10277&whichpage...Easter,SealsAnd here's one thread (of many) that specifically discusses Christmas Seals:
https://goscf.com/t/10829&SearchTer...istmas,SealsGenerally, these items are all considered "cinderellas" (having no postal validity, but still collectible as a stamp not used for payment of postage) and many threads on the subject can be found under that topic on Stamp Collecting Forum.
Many non-profit organizations have also created seals as fund raising efforts through the years, most of which are referred to as "charity stamps". These items can encompass a whole range of organizations such as Boys Town, March of Dimes, St. Jude's Children's Hospital, etc., and were often used during the holiday seasons as promotional material encouraging recipients to make a donation to a given charity.