Long time lurking on the thread.
For me the key is do I receive a personalised service.
HI buffet breakfast - no tip.
IC person taking care of me (breakfast, afternoon tee, happy your) I always tip.
Usually breakfast is chosen as welcome amenity, but this is no factor I do like to appreciate the personal effort.
I am fortunate not to receive vouchers asking for tips, hope this will continue with my current and future visits.