
This is the first year though when I've stopped and thought, but is this relevant, and in the long term, beneficial to those sites?

I've not been in a situation like this myself, as venues I've worked at previously have held workshops (Make Easter bonnets for the Market Place parade) or activities (Egg and spoon races, sack races) which haven't used the venue and contents directly, but rather have tapped into traditional pastimes appropriate to the venue and it's location.
My gut feeling though, is that a generic Easter event may get feet through doors over Easter, but may not encourage a high visitor engagement with the venue, and therefore the venue becomes somewhere only to visit for it's events - not for it's intrinsic values. When attracting visitors with an event, the big 'win' should be that those visitors then engage and enjoy the venue sufficiently to want to return in the future for the venue itself, rather than waiting for the next holiday event to be held.