Sorry in advance for the long post, but I am having issues making this decision on my own xD

I have been in love with this sweater blazer (swazer?) for awhile now. I like that it has the structure of a jacket but it seems like it would be comfy like a sweater. The heathered gray color I think would fit well with my ultra-casual lifestyle and I can think of a ton of ways to wear it. Only, it's much more than I spend on an item of clothing usually. I have gift cards and there is a promotion so it would really cost me $20, or I could spend that money on a few other items.

http://bananarepublic.gap.com/.....pid=858873

I guess what I'm wondering is you think it's worth investing in and if you think it would look dated in a few years. What criteria should an investment piece meet?