Yes, i agree. It is a much shorter walk when you use the canoe to reach the castle instead of the airship. But i don't think that it's a useless excercise. Going early( right after you light the earth orb\crystal and get the canoe ) will allow you to control the awesome power of the zeus gauntlet and healstaff. With these items and a few extra levels from PENOP it is now possible to go on a massive goodie hunt...
1. Waterfall. get the CUBE from the robot, and the goodies from the chest
2. Seashrine. go the the upperfloor, talk to the mermaids, collect the goodies, get the SLAB
3. Melmond. have Unne translate the SLAB for you
4. Lefein. Go get the CHIME.
5. MirageTower. clean out the first two treasure rooms.
6. SkyPalace. if you are brave reenter the Tower and make your way for the 5th floor, now collect the ADAMANT and other goodies laying around
7. DwarfCave. Xcaliber is yours!
Now you are the ultimate power enjoy the spoils of victorty and conquer the remaining 3 fiends and Chaos with impunity.