You should absolutely stay in touch with crews who call you in to day play. Always make sure you ask for a call sheet so you know everyone's name. Again, now is the perfect time to reach out and wish them a happy holiday. They are most likely on hiatus, so clearly you're not asking for work, you're simply reconnecting.
Usually with this question, there's the "unspoken" fear of not wanting to appear like you are trying to take someone else's job. If you are at the point in your career, where you need to build up credits as a day player, then make it really clear (in the future not in the holiday card) that you enjoy being their go to guy/girl when they need someone to fill in.
If you're at the point where you have 100 dayplaying credits and you're ready for a full hire, then target crews who are working on hit shows where the exec producer will most likely get a spinoff or another show, and therefore will need an additional crew. For features, target crews that work on big budget films with MANY additional cameras.
For more tips and articles by top entertainment industry career coach, the Greenlight Coach, visit, www.theGreenlightCoachBlog.com