Mrpq, if you can swing it, going during the week in late August is amazing. Super light attendance, especially Tue-Thu in the last two weeks before Labor Day.
If you go that time of year, you'll easily be able to do everything at the park in two days, one night at the Breakers, without Fast Lane. Or, if you want to have a more leisurely time and maybe hit up the water park, too (which has comically light attendance that time of year), you could do three days, two nights at the Breakers. Then you'd have time to maybe chill at the beach a bit during one of the days, or head to downtown Sandusky for dinner one night (this place is good).
You certainly don't *need* to stay at the Breakers to have a good time, but I highly recommend the experience you get there, if the cost is doable. Plus, you save a lot on admission and parking to help offset what can feel like ridiculously high room rates.