I had a similar discussion with a scholarly conservative friend about dyeing the hardboiled eggs for the Passover seder.
On one hand, it is a mitzvah to beautify another mitzvah, and the dyed eggs look beautiful and make the seder table more beautiful and more appealing and special, especially to kids. And as the point of Pesach is to teach the story to your children, things that you do to make it more appealing and memorable are legitimate (unless they would violate some other law).
On the other hand, the dyed hard-boiled eggs are very strongly associated with Easter, and having dyed eggs might seem to blur the lines between Judaism and gentile practices.
My scholarly friend did say that the eggs themselves are not a mitzvah (only a tradition), so the beautification principle did not apply in his view.
Ultimately I posed the question to my 12-year old. She voted in favor of "pretty eggs", so we went that way. We also choose to not decorate them with garish bright colors — we bought eggs that were naturally green and blue and brown and simply enhanced their colors, plus used a little food-safe metallic gold spray, so it wouldn't seem like the most obvious or common Easter eggs.
Note that this is not validated halachikhally, it's just, perhaps, a baraita from our household. :)
Anyway, I think that culturally gingerbread houses are pretty strongly associated with Christmas, although they're not explicitly religious (like a Christmas tree). But if you made a gingerbread house at another time of the year it would not risk blurring the lines — you're clearly just making an edible model house / candy structure. You could also make a Matzah house at Pesach.
