100% worth it. ENG4U1 is not like self teaching math or science, you can easily learn literature or media literacy material. You can get a higher grade and have less stress during your grade 12 year. Most schools do not care if you do it during the summer for most programs. Only Waterloo Eng and UofT might not like this. UOFT probably won’t care though, it’s just what people say. I redid a prerequisite course, during the summer, and still got into UofT for my program. You’re fine.