Kilgore and Joel Sherman are copycats.
My guess would be the Rays would want Espinosa much more than Lombo because Espinosa can play SS (and play it well, I think) and has power and speed, and they are roughly the same in OBP. They would prefer not to lock Zobrist into SS. After all, they've not played him there until they were a bit desperate last year. They aren't shy about high K guys, either. The only real question is whether they sit tight and wait for Hak Ju Lee, get by with Ryan Roberts at 2d for a year, and play Zobrist at SS. I think the Elliot Johnson / Sean Rodriguez era is over. Morse is a nice rent a bat for a year for them, but Espinosa would be the long term piece.
As for the Nats, moving Espinosa gives you a more than adequate solution in Lombo at 2d for a year, with the possibility that Rendon or maybe Kobernus or Renda takes over eventually. Moore / Tracy with Marrero in AAA gives us plenty of coverage for 1st if LaRoche isn't re-signed. Trading Morse and Espinosa does not lock Rendon into 2d either, long term, if RZ has to be moved off 3d. There are back up infielders that can be brought in if we are concerned about depth.
Shields has been a staff leader for a playoff-caliber team for the past 5 seasons. This isn't some 5th starter. It leaves plenty of flexibility for 2015 and probably makes extension of JZ and Strasburg easier than if Grienke is signed. Greinke is getting at least 6 years and over $100MM, and has less big game experience.