IPX 4 is only splash proof
You say that the Magellan CrossoverGPS is waterproof to IPX 4. That rating is only splash proof (see http://en.wikipedia.org/wiki/Ingress_protection_rating ). Normal outdoor use GPS units are waterproof to IPX 7 (full immersion).
I would not consider IPX 4 to be acceptable for outdoor use. If you are taking a GPS unit into the wilderness (even on a country hike), and using it as your only method of navigation, you must be able to rely on it completely, not just in fair weather. The last thing you want is for your navigation to fail just when you are soaked and cold after an unexpected thunderstorm.
When you consider that the people most likely to buy this unit for outdoor use, are those who are inexperienced, and do not know how to navigate in the wilderness with a map and compass, and are unlikely to bring one as a backup, so when their GPS fails, they will be completely stuck, I think it is irresponsible to sell a unit that is only splash proof, as waterproof, and a good choice for outdoor navigation.
As for boating use, it would be foolhardy in the extreme to rely on a non waterproof unit. If you mount this on the deck of a small powerboat or dingy, then it will get a salt water soaking almost every time you use it. Again if stuff goes wrong and you capsize, the last think you want is to be lost as well.