The GPSr might get you close, but not always to the parking area. Consider a cache in the middle of a park, which is surrounded by roads. If you tell your GPSr to follow roads to get to the cache, it will only take you to one of the roads surrounding the park (whichever would put you closest to the cache). So yes, it would get you close, but it's not always right where you want to be. That's where parking coords come into play. Tell your GPSr to take you to those, and you should end up at the right spot everyt time.
I did buy Garmin's TOPO. It's OK, but does not have all of the trails in my area. Is there a way to put custom maps on the 60cxs or modify Garmin's?