We took the hospital-sponsored birthing classes, along with the baby care and breastfeeding classes and even though I'd been reading Ina May all along, I found them to be really helpful for these reasons:
1. It was a comfortable way for my dh to get familiar with the process, be around other dads, and ask questions of someone besides me, which gave him some sense of power and equality in the experience.
2. We're really busy people and this was a few hours out of the week where we dropped everything and focused on our coming baby. After the class we'd go to dinner. It was a special time for us.
3. We were with an OB, then switched to a mw, then ended up in the hospital. I was glad that I was so familiar with that hospital and its philosophies. I live in a part of the country where natural birth is supported, even in hospitals, and I was glad to know that so I didn't go into the hospital feeling super defensive. We also got exposed to the book Pregnancy, Childbirth and the Newborn in our class, which is an excellent, balanced text on things everyone should know about having a baby. We bought our own copy and I routinely recommend it to friends.
4. We did lots of reading, and there were still things I learned in our class that I'd never read before. The thing that stands out for me is transition. I hadn't read about "the calm before the storm," when the contractions slow down before transition, or really heard from someone who'd been through it what to expect from transition. I've heard a lot of women get scared and ask for drugs at that point. For me, even though it was really intense, it was really exciting because I knew I'd be pushing in an hour! That was really important for my stamina and sense of control over the situation.
If you still don't want to take a class, I don't blame you. Sounds like you're really comfortable with what your plan is. I would still recommend you tour the hospital you would transport to in the event that you need to, just so you know what to expect. That really made going to the hospital a lot easier for me and I still had a great birth.