I am a death wizard and have two wands. One fire and one ice, changing depending of enemy.
I used to have a death but realised that is was no good.
Example: I put a death (+30 damage) shield on enemy. He puts a weaknes shield on me (-25). If i want to take the weaknes shield of without loosing pips (saving up for a six pip spell) i use wand. My death shield dissaperes. Not good.
But using another school wand i can take the weaknes shield off, make some damage, save pip and then atack with maximum damage.
You want a wand other than your class wand because it causes your school traps and blades to trigger. For example, say you are fire school and you put a fire blade on yourself and a fire trap on the enemy. If the enemy casts weakness on you and you want to get rid of this weakness, having a class wand will trigger all your traps and blades, whereas having an other school wand will allow you to remove the weakness without triggering traps and blades.
The only situation I can think of to have a class aligned wand is fighting an opposing school enemy. You could use the wand to counter any wards they cast since creatures usually ward themselves for their opposing school.
I don't use my school wand because I spend a lot of time setting up traps and blades from my school. If I get a weakness spell put on me, I like to remove it with my wand since it doesn't eat up a pip.
If I was using my school wand, I would then use up the blades and traps that I took so much time setting up, just to remove the weakness spell!
Reasoning? If you set your traps and charms for a high level spell hit and then, short a pip, use your wand...well all your hard work goes up in smoke if you have the wand from your school. However, if my life wizard was using a fire wand my charms and traps would all still be there ready for me to make the kill.
At a minimum, you will typically carry the wand for your opposition school and your school. Most of the time you will be using the opposing schools wand. A rather long explanation follows below.
Auric's long winded wand exposition:
Your school's wand is helpful for removing wards against your school. Typically, only NPC's from the opposing school or Balance NPC's will shield themselves against your school in PvE play. However, removing those wards will come at the cost of taking down any blades or traps you have put up.
For example, a storm wizard uses a storm wand to take down a storm shield put up by a myth NPC, but in addition to taking down the shield, it also consumes the storm blade he/she was planning to boost the damage of their next Kraken spell with.
Myth's highest damage spells include a shield breaker attack and myth also has a spell that removes wards. Fire has damage over time spells. Ice has a damage over time spell and the ability to absorb wards. All of these make these schools less dependent on having a school wand. Remember though, the wand is a free cast.
Wands that are not from your class are nice for removing charms like weakness and wards like tower shield while preserving your blades and traps. For example, a life wizard uses a myth wand to remove weakness and to take down an opposing NPC's tower shield. This myth wand would not consume any life blades or life traps the life wizard had planned on using.
As mentioned before, Ice, Myth have other ways of dealing with the tower shield, and Storm can remove charms like weakness, however, wands can do this at no casting cost. So, in most cases, if you are consistently making use of traps and blades, it makes sense to use a wand from a different school most of the time.
Wands that are from the opposing school are helpful for taking down wards against the opposing school that are applied before you use a prism.
For example, an ice wizard with an ice blade up is fighting a balance NPC that has just put up its elemental shield spell. The ice wizard uses ice prism to get past the ice shield, then uses a fire wand to remove the fire shield. Now the ice wizard's ice damage will go through, and his/her ice blade is still up. (hopefully I got the order of prism and shield right :? )
Finally, in certain situations, it might be advantageous to go wandless if you have a very fast deck and absolutely have to get off a low casting cost spell in the first couple of rounds. I have not seen a situation where this is really necessary yet, but I suppose it could occur.
In conclusion, wands are very useful, flexible, and in many cases indispensable tools. Wands and other unique card granting items are arguably the most powerful and game changing items currently in existence.
I believe I am the only one here who will vouch on the other side of the debate. I use my own class wand always. I find it is much more mixed and confusing if I use some other classes wand or staff. And I also feel an obligation to show the world how to stay a pure breed in your class. So naturally most of my spells are also in my class. This is not something I truely recommend, just something I wanted to share.