The Cardinals made their biggest move of the offseason so far in trading Jon Jay for Jedd Gyorko, further shifting the Cardinals away from impending free agents and towards a team cost-controlled for multiple years. With Jay gone and Steve Cishek and Peter Bourjos before him, the Cardinals only current player on the 40-man roster not controlled past 2016 is Brandon Moss.
Aquino, a starter to this point, is just 23, but bounced around a bit this past year. He began his career with the Colorado Rockies, but in 2015, he pitched in the organizations of the Toronto Blue Jays, Pittsburgh Pirates, and Cleveland Indians. That the Cardinals have so many free spots on their 40-man roster currently allows them to take a chance on Aquino. Scouting the stat line, he would appear to be a bit of a control artist. walking 5% batters this past season in High-A along with a low 15% strikeout rate.
If you want a bit more than the stat-line, Kiley McDaniel, in his post on the Toronto Blue Jays prospects, put Aquino in his "Others of Note" section:
[S]its 89-91, touching 94 mph with sink, a solid average changeup and average slider; there's 5th starter upside but at least swing man value.
Aquino is unlikely to make an impact anytime soon for St. Louis, but he does provide some more depth for the minor leagues this season. The Cardinals 40-man roster is now at 35 players with plenty of room to add more as the offseason moves forward.
As mentioned above, the Cardinals have every player but Brandon Moss controlled beyond 2016. Recently signed Brayan Pena is around for two seasons, the Cardinals have 2017 options on Matt Holliday, Jaime Garcia, and Jordan Walden while Yadier Molina, Lance Lynn, and Johnny Peralta's contracts run out after 2017.
The chart below shows the Cardinals payroll for 2016 as it stands today, with data from Cot's Contracts and MLB Trade Rumors. Any blank space indicates the player will be at the major league minimum if on the major league roster.
Given the Cardinals stated intention to increase payroll, it is safe to assume the Cardinals are not done spending this offseason.