Q.I am in process of removing around 80-year-old plants from my historic home. Do you recommend augmenting the soil prior to planti
ng the new plants? If the answer is YES to the above question, how do I do that?

Certified GKH Gardening Expert
Yes, it would be nice to enrich the soil before planting again. You can add amendments such as compost and manure. To really bring the soil to peak condition, get a soil test to see what nutrients, if any, are lacking. Your local cooperative extension group can help with that.
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/improving-garden-soil.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/how-to-condition-soil.htm