Dempster just went to the Rangers, which means:
1. He won't get to face the Astros anymore.
2. He will have to face the Angels on a regular basis.
3. He moves from Wrigley Field, the 18th highest Park factor this year, to Rangers Ballpark, the 7th highest Park Factor this year.
4. He faces a DH instead of a pitcher.
I'm sure he'll have much more run support in Texas, but I'd expect Dempster's K rate to drop slightly and for his ERA and WHIP to soar. You've already got three really good outfielders, so I don't think this would be very beneficial for you. Rios is having a great year, but I think targeting Dempster has an above-average chance to hurt you ROS.
12 Team H2H, 4 unrestricted keepers
C - Mike Napoli
1B - Eric Hosmer
2B - Jedd Gyorko
3B - Todd Frazier
SS - Jhonny Peralta
OF - Ryan Braun
OF - Mike Trout
OF - Shin-Soo Choo
UTL - Brett Lawrie
UTL - Adam LaRoche
Bench - Austin Jackson
DL - Aaron Hill Hanley Ramirez
SP - Clayton Kershaw, Madison Bumgarner, Ubaldo Jimenez, Jhoulys Chacin, Ervin Santana
RP - Glen Perkins, Heath Bell, Jose Veras, Ernesto Fireri, Edward Mujica, Carlos Marmol, J.J. Putz
RCL - Cracking the WHIP - Admiral Trey
C - Yadier Molina
1B - Albert Pujols
2B - Jose Altuve
3B - Jedd Gyorko
SS - Jimmy Rollins
MI - Everth Cabrera
CI - Justin Morneau
OF - Jason Heyward, Shin-Soo Choo, Michael Morse, Nick Swisher, Ben Revere
UTL - Kendrys Morales
Bench - Garrett Jones, David Freese
SP - Justin Verlander, Cliff Lee, Ryan Dempster, Ubaldo Jimenez
RP - Jonathan Papelbon, John Axford, Glen Perkins, Ryan Cook, David Robertson