It’s your decision.
I was offered the opportunity to pay for photos from an event last year. They were crap and I felt quite insulted that they were charging, in no way could they have been considered to be of professional quality.
Some of those posted above are worthy of paying for as the photographers appear to know what they’re doing.
At the end of the day it’s your money and your choice. The image you linked to is nothing special, it’s not bad. I wouldn’t pay for it personally. You might have other emotional reasons for buying it.