I just looked up the free agent list for last year and there weren't many promising players out there. Nate Solder was the #1 OT available and, according to rotoworld, Pugh was #2 with Smith being 5th. That's a pretty sad group.
The OG group was better but nothing stellar. Norwell was the best followed by Weston Richburg, Josh Sitton, and Josh Kline.
WR's had Robinson, Sammy Watkins, Marquise Lee, and Paul Richardson. Other than Robinson, I think the other guys are very average and were way overpaid.
TE's, would you really have wanted to pay Jimmy Graham 3/30? Trey Burton was likely the best option but was very unproven. He received 4/32 from Chicago.
On the defensive side of the ball it was better but not much and the Cards had a top 10 defense last year(I think) and brought in a defensive minded coach so other than maybe CB(supposedly Wilks's specialty), they probably didn't feel the need to spend big on that side of the ball.