While Kinsler is having a down year, a .700+ ops is something we could really use at 2B and we wouldn't have to give up much with Detroit cutting costs. Castellanos is a young, cost controlled 3B that would bring some stability to the position for years to come. I think with Simmons at SS we can continue to get away with not having elite defense at 3B.
As far as Cain goes, any free agent we pick up will cost major dollars. I feel like Cain has been pretty consistent with getting on base and we need people on base when Trout gets to the plate. I'd rather overpay for Cain and have a consistently good defensive outfield than continue to run a new player out in LF every year and hope for the best.
The key is getting better without depleting our farm system to where it was a couple years ago.