Agree with all this. Cash and Targett are £10-15 million full backs in a division where the top full backs are two to three times that value. Like you say, they have both good and bad elements to their game and are inconsistent, that's why they cost what they did.
Will be interesting to see if they are to be replaced if the aim is to move up to places 6 to 8 rather than midtable. Also as their positions are now really important for the way the team plays.