Thanks for the replies. The basic problem was that Photoshop took a bunch of memory and never seemed to give it back, even when the large files were closed. The machine gradually slows to a crawl with spinning beachballs. Looking at activity monitor shows decreasing amounts of free memory until it would get down to 10-15MB, that's MB, not GB, and be soooo slow that I'd need to quite PS and or LR, restart them to get things going again. Memory for this machine is expensive, OWC charges $640US for an additional 24GB of RAM. That's before adding an SSD, which I know would speed things up.
I suspect there is not a simple fix, short of a new machine. It is over 5 years old, will be 6 this September, so I guess I've gotten my money's worth. The problem, of course is that the new Mac Pro is a new paradigm, a completely different way of organizing one's information. I've enjoyed having my main photo drive (4 TB with 50k images) and back up drives within the computer, out of sight but usable. With the nMP one needs to have a separate Thunderbolt box for the same functionality. All of this, plus the non-trivial cost of the machine, (even a "lowly" quad core, 32GB of RAM, at least 512GB of PCIE based flash storage, $3,800 and Lloyd Chambers recommend a 6 core for an additional $500), really adds up.
Best to all.