This house was built in 1961 and I bought it in 2004. Between 2005 and 2010, I got in the crawlspace and used the foil type duct tape to seal the joints on the ducts, then wrapped them with the foil-faced fiberglass to try and insulate them. I also went through and put foam pipe wrap on the pipes that I could. Unfortunately, many of the water pipes are mounted directly to the bottoms of the floor joists. I started to put some of that R-10 pink styrofoam boards (2" thick) on the main plenum to keep more of the HVAC in the ducts. I got as far as putting the pieces on the top of the plenum but stopped when someone more knowledgeable than me said my water pipes might freeze if I wrapped the entire plenum. Those pipes on the joists would have no protection from the cold, so that job was never finished.
I also put some low voltage lights in the front and put the transformer in the crawl, but I can't remember when I did that. I don't believe that I have been down in over 7 years as there is no need to anymore.