The GCH/DCA entrance/exit is mainly a perk for guests when *entering* the parks... anyone can exit through there at any time.
However, it's only useful if you're already in DCA...I wouldn't go from DL to DCA just to get into GCH through there.

Then again, hubby and I never did check to see the distance of walking from DL into DCA and up to GCH versus DL to DTD to the GCH entrance from DTD...we wanted to but there just wasn't time, so maybe it would make sense, who knows?
PPH has the Lilo and Stitch breakfast in their PCH Grill. Fun times, rice in a rice cooker, you can see Daisy quite often there. GCH has the Chip and Dale breakfast in Storyteller's Cafe. We've seen Koda and Kenai, Terk, and the raccoon from Pocahontas there (why is it so hard for me to remember it's name? every time I go to talk about that breakfast I forget someone's name). And Goofy's Kitchen at the DLH has breakfast and dinner as character meals.
If you're staying at a hotel on harbor, and if you're walking, you'd just walk as though you're going to DL/DCA, then go into DTD and make your way to a hotel. With Storyteller's, obviously go into GCH. Actually for the Lilo/Stitch breakfast you'd probably want to go into GCH then exit through their main entrance with the big lovely stained glass (or maybe plastic, LOL) sliding doors, and cross the street to PPH. For DLH just walk on through DownTown Disney until you see the hotel and follow the signs. Of course you could drive in and park for a certain period of time at the hotel during your meal.