I'm sure I'm not the first to see this and ponder the idea, so I thought I'd compare him to Cedeno and see if Lugo would be a better option going forward.
Lugo clearly has a large advantage at the plate. Though he has never been all that good offensively, for the rest of the season, ZIPS projects a .324 wOBA. Over ~320 PA, this would put him at -1.7 wRAA. Ronny is (very generously, in my opinion) projected to have a .286 wOBA. Over the same amount of PA, that puts him at -12.2 wRAA.
So, does Ronny's defense make up for the 10.5 run difference? Depends on how optimistic you are on Lugo's defense. Lugo, since coming back from surgery, has been terrible. His -43.2 UZR/150 is a product mainly of SSS, but closer examination shows that his range just hasn't come back. While his range is generally worth around 5 runs above average, it has dropped to -5.3 since his return. Over at Fangraphs, R.J. says he expects -10 UZR/150 to be more realistic. Ronny meanwhile is on pace for 11.1 UZR/150. Over roughly 75 games, this would put the difference in defense at about 10.5 runs.
Essentially, it looks to be a wash. This is assuming, of course, Ronny lives up to his optimistic ZIPS projection and Lugo's range hasn't deserted him completely. Also, I am not educated in park factors, but I'm assuming Lugo's switch from Fenway to Safeco may actually give Ronny the advantage.