Felix
If the price is right, it is an investment. You can buy it, enjoy having it, and eventually at least get you money back if the timing is right.
Although Lefty bows generally sell cheaper than righties, I would think that a lefty Bear Signature riser is going to be a rare commodity, lots harder to find than a rightie, and therefore more "in demand" than a rightie. You might have a tough time making a swap.
JUST MY THOUGHTS.