I think the Monorail can be a lot of fun, but it can also be pretty time consuming...it's just a matter of luck and timing. If you get there right when a monorail arrives, then it'll probably be faster than walking. However, if you just miss the monorail and have to wait for the next one, walking might be faster. While you'd think they'd run multiple monorails, I have been there when there was only one on the track, so it might mean waiting for as much as a full trip if you aren't lucky with the timing. So if you have time, I would consider taking the monorail, but if you are running short on time and/or want to have more control over when you get to PCH Grill, I would walk.
I was surprised, but the monorail doesn't save as much walking as I thought it did. It came out to be about 0.3 miles from the monorail station to PPH lobby and 0.5 miles from the DL main entrance to the PPH (via the GCH). Assuming you're starting in Fantasyland, just behind the carousel, it's 0.3 miles to the main entrance or to the monorail loading platform (roughly equal). So all in all, difference between the two routes is about 0.2 miles (or about three football fields). I would have thought it was more than that...Interesting!