Is there a "right" time to buy camera bodies, both mirrorless in my case as well as DSLRs?
Yes. But like any other camera purchase decision, it will be highly individual, depending on a number of factors, such as what your budget is, what your needs are, and how much you care about specific aspects of image quality. For some people, with purchasing full frame, the answer may be "now", for some it may be "next year", for some it may be "never".
Full frame is not the ultimate end-goal of every digital shooter, despite the fact that it's often touted as such.
The only real timing advice I can give is that most of the new-camera product announcements tend to cluster around the late fall (Oct/Nov) and early spring (Feb/Mar) time frames. That doesn't mean new cameras haven't been announced in the summertime. But these seem to be the clusters, usually around a large camera product show. So, right before those time periods, you may want to hold off to see what's in this specific cycle. But nobody can predict with any accuracy what's coming down the pipe, which is why rumors sites can be such fun. Just take all the "announcements" with a grain of salt--particularly the ones that smell a great deal of "wishful thinking."
Related, are full frame bodies discounted during the holiday season or is that limited only to entry level bodies and older full frame bodies?
Discounts basically happen if a body is about to become discontinued, or you can find a deal on a used/refurbished one (I picked up my 5DMkII through the Canon Loyalty Program's deal on refurbed copies). But all cameras tend to depreciate over their product life cycles, even when brand new. Some do so more slowly than others--super "hot" or popular items may never drop at all, or only a small amount--but most will be substantially lower in price at the time they're discontinued and replaced by a new model that's likely to be priced back up at the beginning of the cycle (or possibly higher).
I suggest using the camelcamelcamel.com site to view the Amazon price history of any given camera body, and you'll see a downward trend over time. This is also shadowed on the used market. Few camera prices ever "drop off a cliff" for one reason or another, but will see a gentle, steady, downward trend over time as it gets farther and farther from the point of introduction.
As with cellphones and computers, the nearer you are to the beginning of the cycle, the more you'll pay, but the more time you'll have to enjoy the features. The later you are to the end of the cycle, the less you'll pay, but the more likely you may be to go jonesing after the replacement. :)