pros:
-can do a decent amount of damage at the middle gs range (5.5k – 6.0k), quite better than some 4t10 5.5k gs mage, who lacks crit and who will have lower 2t10 uptime
-high spirit value that greatly benefits from the 10% buff and 10% talent (and 3% racial if HU)
-high spirit value provides decent mana regen but you can still go OOM. I'm not sure at which point 3/3 spirit is better than 3/3 of 30% mana refund, but from my experience it feels like 1300-1400 spirit is the value
cons:
-to a degree it's a meme gear composition, so people will “wtf” you a lot
-at higher gs numbers 4t10 will start outperforming your gear, but you will have a hard time switching your gear composition to a different way. So there might be some delay in switching gear and hence a loss in your dps
also a small example, to show the idea. If you are comparing [Crushing Coldwraith Belt] with [Lingering Illness] (both 277 ilvl), there will be a difference of 90 haste and 90 spirit. For spirit you get 0.7*(90+90*0.23) (for human) = 77.5 crit rating. In fact, there is actually something else that contributes to the % of spirit, so it will be like 80 crit rating which is just 10 points smaller than 90 haste. While still getting regen from that spirit.
Running some Crit/Spirit-Items isn't exactly uncommon even with 4pt10 people at or near BiS e.g. it's normal to run Lingering Illness, Nightmare Ender and sometimes even Ring of Maddening Whispers depending on how the mage in question balances haste. Some run more. Some less. A lot of it boils down to personal preference.
But honestly not sure why you mention things like 3/3 student of mind or 3/3 master of elements like they're mutually exclusive. You can (and probably will) run both anyways if you intend to run more spirit.