If were talking overall, LaRoche isn't much of a downgrade at all from Dunn.
Dunn is a better offensive player, mainly because hell hit more bombs. LaRoche will not compare there but does in most other categories.
Defensively, LaRoche is twice the defender Dunn is.
So overall, I think the impact will be similar. Couple less runs, but well save a few more on the defensive end.
I also don't see how you can compare Morse and LaRoche. LaRoche is proven over 5+ years as a starter. Morse had a solid year lasy year as a utility guy. LaRoche is a definite upgrade if Morse is the alternative.
Let's just hope we get LaRoche done. I thin him being left handed makes him a better fit for the lineup, but I would have preferred Lee for one year.
Morse's career v LHP is .313 / .375 / .518 . Granted, it's over only about a half a season's PAs (248), but with a AAA line over 1287 PAs of .292 / .354 / .461 against all pitching, I'm very, very comfortable saying he has to play v. LHP. If it's over LaRoche at first (career 888 PAs, .254 / .308 / .446 v. LHP), then do it, and get a lefty masher OF to yank either Roger or Nyjer out of the line up, or, if that is too much, then just play Morse in the OF over one of those two v. LHP. But Morse absolutely must plan v. LHP.