All depends on how you monetize holiday domains; I have minisites on them with adsense and Amazon stores. Unfortunately I don't have any Christmas names... but they work pretty much the same as any other holiday name, they should make you some steady minimal income the rest of the year, and 'spike' during that holiday.
For example, I have a couple good Halloween domains, for generic Halloween products. They average anywhere from $15 - 75 per month the rest of the year, but in Sept and Oct each one makes about $450. That's almost 1K a month for two minisites. Spikes are nice.
All boils down to how well your names do during the spike, and how well they average the rest of the year. Some are worth it, some aren't. Parked, they aren't worth it unless you get decent type in traffic. Developed as minisites or better, it can be well worth having holiday-related names.