Best way to navigate the Peloponnese

Do you have plans other than Mystras for your time in Sparta? Mystras does cover a fair amount of ground, and it's on the side of a hill, so it needs some time. Sparta, though, is quite modern. There may be all sorts of interesting things in that area (I didn't have a car, so I didn't explore), but two nights probably wouldn't be necessary just for Mystras.

I'd keep Dmitsana at the end because it was such an easy and pleasant drive back to ATH from there. I agree the trip could use some fine tuning, but of course it depends on what you wanted to see in each place. Perhaps add what you wanted to see in Sparta and Kalamata, as those are often skipped. I'm a hiker, so I stayed longer in Kardamyli, and you can definitely stay longer in Nafplio and not be bored.
I tried to organize my trip where I could stop en route between some places and have stays of at least three nights most nights, minimizing one and two night stays. (those are necessary sometimes, but a series of them is exhausting). It's a wondrous area, good luck!
I drove from Kardamyli to Dmitsana via Messene, and the drive was somewhat intense at the end (I wondered if we got off track somehow). Consult viamichelin carefully.

Thank-you for your help and insights! I’m attempting to find any long lost relatives in the Sparta area. Don’t know how far I will get but it’s a good excuse for travel.
Neapoli apparently has some caves in Kastania I believe and Pavlopetri is the largest discovered underwater archaeological site ever. Those are my reasons for going there.
Any islands in the Saronic Gulf you could recommend for a visit? And any budget accomadations in the Peleponnese???

Much appreciation for all these tips. My biggest problem seems to be the drive from Nafphilo to Monemvasia. I really want to drive from Leonidio/Geraki and go through Gerakas to see the fjord and then Monemvasia. Am I crazy and want to do everything?? Is this possible to drive in one day?? Maybe I should go Nafphilo-Gythio and use that as a base for Vatica Peninsula??
Second concern, is Kardamyli the place to be on that peninsula??? Maybe base in Kalamata to do Messenae, Eyes of Venice, Kardymyli coast??Kalamata looks like big touristy city that the Brits seem to like. Talk me into it

Kardamyli an Kalamata are about 25 miles apart. I do not see a reason to spend time in both. Pick one and save the bother of packing in/out of the hotels

On the RS tour we drove through Kalamata and stayed in Kardamyli.

I never had a 'wish we had stayed in Kalmata' thought.

Admittedly not an in depth comparison of the 2.

I totally agree with nick s comment upon. It s the best option.

Lots of good advice here. I might add that you could consider spending a bit more time in Corinth area. There is the canal, Ancient Nemia, Ancient Corinth as well as the magnificent fortress at AcroCorinth.
Our last trip we spent a week in the Peloponnese. Perhaps some images will whet your appetite.
Corinth Area. https://www.flickr.com/photos/stanbr54/albums/72157711755443483
Peloponnese, Mani and Monemvassia. https://www.flickr.com/photos/stanbr54/albums/72157711323535897

I think if you are looking or a more convenient base for your driving plans, there are more convenient places than Kalamata or Kardamyli--I just don't know them after only one trip. (If it is okay to suggest this here, this area gets good coverage on the Trip Advisor forum if you want to ask there too).
Some discount Kardamyli as "touristy," but in late May I just found it pleasant, and for hiking it was a great base. I would not want to make the drive in and out of every day. We only took one day trip, and that was just because it rained.
It was definitely challenging to decide what to see and what to skip--I'll be returning one day for sure!