| Nillin |
The only real problem I see with the Universalist Wizard is the lack of a 1st level passive power, mainly because this passive power that the specialists gain becomes drastically more powerful at level 20. Here are three of them,
Abjuration
You gain resistance 5 to an energy type of your choice, chosen when you prepare spells. This resistance can be changed each day. At 11th level, this resistance increases to 10. At 20th level, this resistance changes to immunity to the chosen energy type.
Conjuration
Whenever you cast a conjuration (summoning) spell, increase the duration by a number of rounds equal to 1/2 your wizard level (minimum 1). This increase is not doubled by Extend Spell. At 20th level, you can change the duration of all summon monster spells to permanent. You can have no more than one summon monster spell made permanent in this way at one time. If you designate another summon monster spell as permanent, the previous spell immediately ends.
Divination
You can always act in the surprise round even if you fail to make a Perception roll to notice a foe, but you are still considered flat-footed until you take an action. In addition, you receive a bonus on initiative checks equal to 1/2 your wizard level (minimum +1). At 20th level, anytime you roll initiative, assume the roll resulted in a natural 20.
These abilities all feed into the idea in Pathfinder that if you devote all 20 levels to a single class you get some sort of capstone ability, and for a specialist wizard that's true. I'm not sure what exactly would be appropriate for a universalist wizard but I will say that I don't think they need extra spell slots just a nice passive ability that can top them off at level 20.