Saying no to miscellaneous administrative tasks as a Grad student
Will there be any negative repercussions if I do that (reject majority of the tasks)?


Of course there is no way to say for sure whether there will be any negative repercussions if you keep rejecting those requests. However, frankly, it seems likely to me that:


You will come across as kind of an ass to the administrative staff, and that's not great at all. If your university is at all like mine, there will be a number of times when you need their support in, well, administrative matters, and you will be very low on their priorities list if you make it a point to never or rarely help them out.
You will come across as kind of an ass to the other students, who will surely notice that you never help out and they need to take on more of those duties as a consequence. You will invariably need their help at some point during your studies, and it's not unlikely that they will not be thrilled to help you out then either.
You may come across as kind of an ass to the faculty, which tends to notice if certain students are never volunteering for anything. The extent to which they care is another question, but it seems unlikely that they will consider this a positive attitude. In the worst case, somebody may remember this when the time for letters of recommendation comes up after graduation.



  Also are there any tips on how to say no, with respect to Academia? I may try a new strategy of ignoring such emails, the emails do "require" us to respond whether we can make it or not, not sure if ignoring such emails may be a better policy since I think that is what some students do.


If you really think you should keep on saying "no" to those things, it seems fair to tell the administrators directly that you are not available for volunteer work. They will likely be annoyed, but they will also be annoyed if you keep turning them down. I don't think there is a way to turn them down without annoying them in any way.

(and please don't start stringing together increasingly less plausible excuses - that's just childish)