I can speak for the Magic Carpet Spirea. We also had that cold snap after above seasonal temps. I have had multiple bushes where the new growth was burned/browned. As for my spirea's, I just pruned them hard as I do every year to keep them contained, and they are coming back just fine. In my experience Spirea's can take a lot of abuse and still come back. As for the hydrangea, I don't have the Lady in Red variety, but my Annabelle and few others were also pruned hard, I cut mine back to about 12 inches as recommended to me for proper growth. Now mine bloom on new wood, so before you prune I would be sure to check on whether yours blooms on new or old wood. If you do prune, cut right above a new bud/leave area. Hope I have not given you any incorrect advice, but this is what has worked for me. Good luck.

I watered my mature roses about every three to four weeks and watered the babies about 2x a month. By the beginning of August, I thought I was going to lose most of my roses - they looked terrible. However, almost all of them survived. I have had to prune a lot of dead limbs but overall, they look fabulous. My teas (e.g., Mrs. B.R. Cant, Rhodologue Jules Gravereaux, Georgetown Tea) are currently in overdrive, the chinas (e.g. Old Blush, cl. Martha Gonzales, Louis Phillipe) are thriving, the Hybrid Musks actually never seemed to notice the drought, the Rugosas thrived, my climbers did have die back but are currently very happy and seem to have definite thoughts about world domination, and even the bourbons survived (my bourbons are a little more frail and water dependent. Maggie is not happy but she is alive. Zephrine had significant die-back but is going to be OK). We have had a lot of rain this spring (I am north of Ft. Worth) and the roses are responding beautifully. My mature fruit trees are not doing well, however, and many will probably die. My cedar elms and oaks are fine and they were not watered. My pines are fine. We do have a stock tank for the livestock that almost went dry but did not and that helped the local wildlife.

I'd bet the smaller number of flowers is perhaps drought damage, but the bigger concern long-term is the leaf browning, which around here is likely anthracnose, and, unfortunately, for a dogwood it's usually a death sentence. Oaks and Sycamores can live a hundred years with repeated anthracnose infections, but dogwoods are usually goners, IIRC.

First, Meyers are extremely resilient; it will live. DO NOT prune it; as the tree needs the carbohydrates in the trunk and limbs to recover. In time the tree will sprout again from the center and fill in the gaps. DO take off all the fruit; if not the tree will sacrifice everything to save the fruit. Keep a good thought.