Think of it like an investment, if you've put down money for the product you're much more likely to make a real go of your work; not to mention have a bit of motivation for making some possible revenue.
Frankly I'm amazed Scirra not only offer a free version of Construct 2, but also how fully featured it is: A 100 event limit and the exclusion of families barely dents the stupendous creative potential within the program; this reason alone was the reason I put down the cash for the product, very impressed with the quality up front and wanted to support.
As for the price... I can't really empathise, at ?50 that's just over a days work for even the lowest paid job, and in comparison with the price of similar software, mindblowing. Even student versions of popular software can still cost triple figures, the price is bargain.
An interesting route might be a freeium version of Construct 2, where you pay to unlock features like famalies and event limits, but at the lower levels any money you make with your games generates a cut for Scirra; from what I've seen I can't see them running with the idea, but it's one I'd fully support.