Onsite all the way!
I've stayed budget ($40 a night and driving 15 minutes in), $80 maingate and walking, at PPH for about $350, and I've also flown in for the day and not gotten a hotel.
Personally I think if your party has 2+ people, and you plan to visit for multiple days, staying onsite is 100% worth it. Not just because of magical mornings, or getting a fancy lanyard and pin set, but because it is so much easier to start and end the day if you don't have that far to go. You won't think it makes a difference. After day two, it makes a difference.
I haven't stayed at GC yet, but the difference between PPH and maingate - I wouldn't do maingate again unless I was very seriously on a budget. My favorite way to visit is to get the earliest flight, fly down from Northern California in the morning, Uber over, spend the day in DL, get picked up at the Disneyland Hotel by Uber, and fly back home. I save up my airline miles so my flight is basically free and I only pay for my Uber and my Disney ticket. It's about $350 for the total trip.
Yes, you do pay more to stay "onsite" but personally I think all the perks make it worth it.