I kept my rare tulips and pansies too! I only have had half my garden growing with the new flowers for butterfly spawning, but I've had many friends come by to cross-pollinate so it seems they appreciate that too. They seem to be trying for the shirts and furniture from those flowers, so I bet they're happy some people left the older garden flowers up.
Edit: I think one of the most amazing things about this event is how I know none of these in-game friends irl, we've not made plans about gardening and stuff, yet we have all stuck together to get through this.