I want the paralyze spell, maybe. With or without it, is it worth all the perks like Illusion, or no?

If you just want paralyze spells, you essentially need the Expert level perk. In my opinion, I think it is worth it to fill the tree. Atronach is incredibly useful and the master level Alteration spells are pretty good (Mass Paralysis and Dragonskin). If you are not a mage, don't put points into Mage Armor, which is probably obvious anyway and I wouldn't get the dual cast perk either, as it only increases the duration of the effects, not the magnitude of the armor.

I've found that Alteration is the school I use most in Skyrim with my mages and the perks are great. If all you want to do is Paralyze though, you might be happy just getting the Staff of Paralysis. It won't involve taking perks to use it. I use the spell and give the staff to Argis and we have lots of fun. Just go to

and it can be yours. If you need to see exactly how to get it, here's a video.
http://www.youtube.com/watch?v=A6Phm1A5qQU

You gotta go all the way. Maybe you can ignore the Master perk.

I would say don't get the atronach perk of you are a conjuration mage, because there is a well known glitch with that perk. Other than that, get all the way up to the expert perk

If you play pc there is a mod call unofficial patch you can install that fix this bug

My main character uses Alteration. Paralyze is a incredibly useful spell to use if you're surrounded by a bunch of enemies. Hit the leader, take out the followers and 1v1 the leader enemy. The armor spells are pretty neat too.