Two thoughts:
a) It depends on what you mean by “celebrate”. For instance, Hanukkah celebrates the re-dedication of the Temple, that Judaism was not wiped out and that God showed favor on the re-dedication by providing the miracle necessary for it to take place. This was a good deal before the Incarnation (it is recorded in Maccabees, which Catholics still have in the Scriptural canon) so…so far, so good.
But if you recite or sing the traditional Hebrew prayers of Hanukkah–and what would Hanukkah be without these?–you’ll find that they say this, in translation:
*Blessed are You, Lord our God, King of the Universe, Who has sanctified us with His commandments, and has commanded us to light the Chanukah lamps.
Blessed are You, Lord our God, King of the Universe, Who has done miracles for our fathers in bygone days, at this time.
Blessed are You, Lord our God, King of the Universe, Who has given us life, and has sustained us, and has brought us to this time.*
Now, I think the third prayer, the Shehecheyanu, is a really nice one, and one a Catholic could easily use on a regular basis. The second one is nice, too: this is a miracle we have in our Scriptures, still, and so to remember it with gratitude is a good thing.
But with regards to the first prayer: we Catholics do not believe we are sanctified by the Law, but by the death and resurrection of Jesus Christ. Furthermore, not even the Jews believe that we Catholics (or any other gentiles) are commanded to light Hanukah lamps. We’re not. As a rule, Jews don’t go around saying prayers that don’t fit. You say the ones that a situation calls for, once and once only, then you stop.
So if you were to “celebrate” Hanukah, you’d have to do it in an altered form, or it wouldn’t fit you.
Which brings up
b) Jews are not necessarily going to find it respectful to know that Gentiles outside Judaism are making up new personal rituals based on Jewish ones. (As in our own side of things, the Orthodox are not even particularly thrilled when Reform Jews do this!) This is particularly true for the Seder, by the way. If you put yourself in their shoes, and imagine someone making up a personal version of the Mass, you can see their point of view. Even if somebody made up a set of prayers that used our Rosary, it wouldn’t be right for them to have a Crucifix on their “rosary” when they didn’t put their faith in the death and resurrection of Jesus. So one has to tread very carefully, in order to be respectful of others. “What they don’t know won’t hurt them” does not fly here. Do not do in private what you would not want shouted from the rooftops.
I think it a nice gesture to fast for the sake of the Jews on Yom Kippur. I think they’d consider that a mitzvah, and you a mensch for wanting to do it. Nobody is going to care if you break your fast in the manner they would, either. But do be mindful that your religious rituals must always worship God in keeping with the truth God has revealed to you, and always do so in a way that is not in any way insensitive to those who do not enjoy the fullness of revelation.
I think Jews and Muslims would both be pleased if we were to educate our children about their holy days and why they keep them, just as we would be pleased if they were to take the trouble to learn and teach what we do and believe, and why. They would be pleased if we were to commend them particularly to Heaven on their holy days, as we would if they did so for us. It has to be done in a very careful way, though, particularly if anything in the way of actual co-observance is planned. This isn’t something one just jumps into because we like latkes, doughnuts, and the pretty candles. We have to consider God’s will for us and gifts to us and his will for others, and proceed accordingly, with that big picture in mind.
