If you spam the Event markup, you’re at risk of getting a penalty from Google. Trying to trick Google into showing rich results for non-events like coupons, may trigger a manual action:
“we’ve been receiving feedback from users seeing non-events like coupons or vouchers showing up in search results where “events” snippets appear. This is really confusing for users and also against our guidelines… Since this creates a misleading user experience, we may take manual action on such cases” – source (Google)
I just love it when Google is explicit about a ranking factor, or a penalty trigger. There’s no need to write X,000-word article to explain why you shouldn’t be doing something.