He's only 24 and showed in 2009 that he's got plenty of utility value, especially in the future. However, his best asset is he's a footballer not just an athlete like a whole host of other wingers hence why he pops up in the right place at the right time. Tigers preliminary final comes to mind.
Anyway, the length of his deal may have been for cap reasons. For instance instead of offering him 3 year deal at $660K ($220 a year) he is offered a 4 year $800K deal ($200K a year) releasing 60K over the first 3 years for someone else. 60K here and there is a fringe player giving quality depth.
By the way, the above numbers are hypothetical. In reality, after scoring a double in the GF, he's worth millions