Unless it is a VERY VERY crowded time of year, you should have no problem boarding any Disney bus, monorail, or boat, and going to any resort on property.
Occasionally, at closing time there will be someone stationed at the resort monorail at the Magic Kingdom to check resort IDs. That is the only time I have ever seen someone ask for ID for transportation.
We do stay onsite, but instead of going back to All-Stars for our break, we go to a different resort every day and have lunch, stroll the gardens, and relax at the tables near the pool bar.
Another note, you can shop at the resorts, eat at their restaurants, stroll their gardens and public areas, rent boats, bikes, fishing poles, play golf or tennis, etc.
However, you cannot use the pools or hot tubs unless you are a guest staying at that resort.
Hope this helps.
Carol