The effects of redistricting are overrated.
It's generally agreed that congressional districts should be geographically contiguous, and that when possible communities should not be divided within congressional districts. With geographic sorting, people have come to live near those who agree with them politically. Rural Arkansas will be very conservative. Harlem will be a safe Democratic seat.
The sorting benefits Republicans. Liberals are more likely to live in areas where their candidate gets more of the vote, or in small enclaves within conservative regions (ie- college towns in Nebraska.) John Sides and Eric McGhee of the Post argued that the post 2010-redistricting (when Republicans gained control of numerous states) didn't actually help them with any net house seats in 2012.
http://www.washingtonpost.com/blogs/wonkblog/wp/2013/02/17/redistricting-didnt-win-republicans-the-house/The counterargument would be that Democrats might need to gerrymander just to be even with Republicans in the House, although that's not an argument anyone representative of the party wants to make.
