Biochem II was one of the most interesting courses I ever took. I don't think it would hurt to take it. The whole thing about taking these classes is not only to prepare for dental school, but to make yourself look appealing to dental schools. If you are going to take it and get an A or a B, then go for it! If you think you might get a C, then skip it. Biochem is very similar to Organic, so if you didn't do too well in that course, it's a strong indicator that you might not do so hot in Biochem.
Ultimately, the choice is yours. Good luck!