I think frum people should be showing hakaros hatov. Years ago I used to make it my business to attend memorial days parades and thank the veterans. In Dorash Moshe there is speech given by Rav Moshe Feinstein in honor of July 4th. Today a similar speech on July 4th from a major gadol would be unthinkable.
But it’s not only the frum world where the attitude of appreciation to the US has changed America has become so polarized, there is so much anti America sentiment among the non-Jews that memorial day is little more than any other secular holiday like presidents day that is just ignored in the context of having meaning by everyone Jew and non-Jew alike.
48 year the US centennial was a major celebration year. (look at the quarters) In two years from now is the Semiquincentennial (250 years of the US) There are no plans for celebration. There are no bipartisan committees (remember those) working on making it a memorable event.
The frum world is not going to show more appreciation than the non-Jews do