First off, if you're just there for the summer, skip the the visa.
No. Don't skip the visa requirements. If you're caught (and this isn't impossible, the Straż Graniczna like to look through passports) - then a ban from Schengen could happen very easily. Being banned from the Schengen zone is effectively rendering you persona non grata throughout a huge chunk of Europe - and may force you to apply for a visa for any subsequent vists, with a hell of a job to explain just why you overstayed.
It's also a recipe for disaster if you're stopped by the police - it's not completely unrealistic to assume that they might want to see your ID - and if you're found to have overstayed, deportation will follow.
There's enough anecdotes online of people caught and thrown out to make it not worth the risk.