| Omen |
Omen's take - More resources is the answer.
You posit that a 9th level wizard that is down to his 3rd level and below spells should rest. So, how many 4th and 5th level spells should a 9th level wizard have? Is there really a large contingent of players that thinks that the spellcasters need to be made MORE powerful?
I'm not advocating more power for spellcasters (God no!). I'm saying that, when a spellcaster has blown through his higher-level (i.e., "level-appropriate") spells, the [u]tactically sound[/u] thing to do is to rest and them. It's neither heroic nor dramatic, and this is a problem, but it's smart.
A 9th-level wizard will be facing things like bone devils, frost giants, vrocks and greater elementals. There's a very good chance he's end up facing things like bebeliths, stone golems, eleven-headed pyrohydras, beholders, glabrezus and death slaadi. He needs potent spells to deal with these dangers; if he's reduced to plinking away with magic missile and scorching ray, he's not only in trouble - the whole party's in trouble.
The OP made a suggestion, and I am shooting it down because I feel it's an unfair solution to punish players for failing to adhere to an arbitrary standard. Personally, I would like some variant on Werecorpse's idea, where spells come back faster than every 24 hours. Obviously this would need to be carefully designed to keep casters feom becoming even more gawdlike than they already are. My personal take (of the top of my head) would be: with a 5 minute rest, a caster regains all the spells he has cast except for one of the highest level. So, if my 9th-level wizard cast 2 5th, 2 4th and a 3rd, I could sit for 5 minutes and regain the 3rd, the 4th, and one of the 5th - I'm down a 5th-level spell for the encounter.
(Note that this is a spur-of-the-moment idea and has NOT been tested in any way)
Also, I hate the idea of modifying treasure. It's equally unfair and arbitrary and it leads to bizarre and counterintuitive results, where the monsters you meet later in the day just *have* more treasure than the earlier ones, for no apparent reason. It's particularly bad for a GM like me, who usually designs all the treasure before the game ever starts.