For the record, I've banned druids until I can balance them.
I do have one psion in the game, but it hasn't proven unbalancing yet.
I'm still looking for a way to limit the cleric spells.(any suggestions welcome)
I could, of course, do the same as with the wizard, but the campaign has been underway for quite some time now, and the cleric has up to now allways has access to all cleric spells.
There are no sorcerers yet, and they will also need to obtain spells (through contacting demons, as mentioned before)
I have already discussed it with the player playing the wizard, and he has accepted the rule for now, as long as he feels he's receiving enough oppertunity and money to get the spells he nees/wants.
On the subject of having to spent downtime: he's planning to build a Craft-heavy wizard, so he's already counting on down time, which I plan to give him.
There is no time-constraint on the campaign I'm running, so downtime won't be an issue.
Regarding getting enough gold: they have already spent ressurrection costs on this player twice, once to get his third character raised, and then when he realisde ressurrection was available (it had just become available in the campaign) again to get is first character raised. Sharing gold is not really an issue in this group, so I expect it not to become one in the future.
Also, because of the way I handle spell preparation, a memorized spell is not 'forgotten' when cast. This means a wizard could use a found spellbook to memorize the spell (trying again the next day when it fails) until he has the time and money to copy it. He only has to get it right once, or until he needs the spell(known)slot to prepare another spell.