Has your Wizard expressed a lack of options or potency? Has he offered you suggestions for rules modifications? One of mine has. Please read, contemplate, and offer feedback if the mood strikes.
Problem: Can’t prepare many spells, and non-cantrips never get easier.
Solution [a]: Prep limit of level +1 replaced by mana points equal to 2xLevel+INT. Spend points per level of spell you wish to cast, and get them back from rests or similar. (gives more options on the menu, but fewer castings of the expensive ones)
Solution [b]: Prep limit as normal, but rising cantrip threshold (gives more freebies as you level, so a level 2 spell is a cantrip to a level 7 wizard, etc)
Appendix: Either of these options could include being allowed to cast beyond your level at a higher risk.