That's an easy one, more park days for sure. We try to go 1-2 times per year, and we've never stayed onsite. Even knowing we'll be back, I still can't bring myself to sacrifice park days for onsite hotels. It's just not enough of a benefit to outweigh what you miss in the parks. Especially as busy as the parks have been lately, you'll want the extra days to see everything and not feel rushed.
We also prefer to stay in a suite, but have never stayed at DI&S. We typically stay at either the Embassy Suites South, or the Anaheim Marriott Suites. I can usually book the Marriott suites for around $75-90/night for a 1 bedroom suite. We drive, though, and always have a car. Not sure I'd want to walk that distance to the park. But, they do have a shuttle that picks up right at the hotel, so that's an option, too. We have also stayed at the Dolphin Cove Resort, which isn't walkable to the park entrance, but is walkable to the parking lot, and you can grab the Disney bus from there.