The GC will cost 24-39 (19-30 for DLH)for a standard view in the off season, or $240-390 per night at $10 per point. If I had the points paid for and wasn't going to use them at WDW then I wouldn't hesitate to use them. Staying onsite at Disneyland isn't as important as WDW, but still it makes the trip extra special. There are several motels within easy walking distance of the parks, but the quality of the walking distance hotels is not equal to Disney. However they are perfectly nice motels, we have stayed in several of them. The number one most important thing for us is less than 10 minutes walk to the gate with a clean comfortable room. The walk from the Disney hotels is easy. The monorail is (or will be available) but usually walking is the faster.
Why not price out the vacation paying for a room at the GC or DLH and decide if paying or using points is more cost effective? You said you definitely want to stay onsite, so the only way to know which route is cheaper is to price it for yourself.