I love doing the Christmas musical for the theatre I work at the most because it is a 7-11 week run, pending extensions. Tonight is performance #36 of 64 (and possibly more...). I tend to find that casts really tend to bond more during the holiday season than any other time of the year. There is hardly a day that our green room isn't filled with candy and other holiday goodies that various members of the cast and crew bring in. Spirits are usually high which translates to lots of energy on the stage.
Eight shows a week (plus understudy rehearsals, put-ins, brush-ups, etc) can be taxing. If you're lucky enough to have this be your only job, then the hours tend to be manageable and one can keep up with your sleep and have enough energy. If you have another job, you just have to pace yourself and turn down some social engagements to make sure you take care of yourself. But make sure you save some time for yourself and blow off steam. Try to shop for your groceries and do errands on a day when you have to work anyway so you can have a true day off when you have a day off. Try not to answer your phone or check your email on your day off (to this end, have a separate email address for SM related work so that you can still check personal email).
I think we all have those days where we don't want to go to the theatre and do the show. When I have those days I take my iPod with me and listen to music to pump myself up, which tends to get me in the mood to do the show. Try to leave your personal life at the door and put on a smile (or at least a pleasant attitude) when you are around the cast.
In terms of keeping the material fresh for the actors, I find that they will inevitably discover new things and you just have to keep an eye as the show grows to make sure that the new bits are within the world of the show that the director created. Long runs do tend to promote lots of backstage antics, so watch that the games don't end up making their way onstage. Try to be specific in your notes because often when giving a general note actors will assume you are talking about someone else and not them.
I wish you the best with the rest of your run!!