I don't think removing the parameters would be ideal, though, since some sites might legitimately serve up different images based on different parameters.
Just limiting the amount of traffic to a single server, or outbound from a single spreadsheet, seems like a good solution, though.
You see a surprisingly high amount of excel-based bill templates - and you may want to hotlink the company logo or a signature.
Doesn't that somewhat defeat the purpose of a dynamic image?
Moreover, the issue is not about the feature, it's whether Google should limit the number of requests made per image. From other comments it seems like Google is hitting each image hundreds or even thousands of times. I suspect this is for cache? If that's the case, Google should look at better way to handle it. A single fetch and propagate to closest zone should be enough. But this is not a reason to limit the feature (eliminating parameter query).