IMHO - The mist does not work well.
It shrouds your castle so anyone who hovers over it sees only question marks for owner/name/might/alliance/etc. Unfortunately, if they scout you, they see you; if they attack you, you win or lose same as always.
Using a portal to relocate your castle enshrouds the plain you leave and your newly located castle in mist. If, however you want to attack or scout, even a wilderness, you lose the mist.
If your goal is to truly hide your castle, having mist on it may do the opposite. For large players, the misty castles are too tempting to resist scouting and for large alliances, who can afford to assign one player per quadrant to scan for misty castles, it makes it all the easier for them to find you in your new locale!
Lastly, there is a glitch that currently makes your wildernesses show up as unowned, so you may - especially in full domains or if your wilds are level 10 - find your wildernesses are under attack.