Our group has been playing C&C for about eight months now and are up to about sixth level. A subject that's come up more and more often is the save vs spells (PHB p.75: "a spell’s challenge level is always equal to its caster’s level unless specified otherwise"). Our players see that as a problem especially with secondary attributes, because assuming enemy spellcasters with the same general level as the PCs, the save will never get better over time: adding the PC's level but subtracting the enemy's level will more or less cancel out.
Why is the save made against caster level rather than spell level? If it were spell level, PCs would have a chance against even very high-level spellcasters, but if it's caster level, the save is difficult even with casters kept to a similar level as the PCs.
Thinking out loud here....
Two 11th level casters with relevant primes dueling use a 3rd level spell.
Using Caster Level: Target # for save = 12+11= 23. Roll needed to save = 11+2+11<. So any roll of 11 or better saves. (1 being an auto fail and hence discounted on the roll).
Using Spell Level: Target # for save = 12+3= 15. Roll needed to save = 3+2+11<. Again, any roll of 11 or better to save.
Splitting between using Caster Level and Spell Level. Target #=15 vs Roll to save= 11+2+2< takes it down to a 2 or better to save. Meaning for an 11th level caster any roll but a 1 succeeds making the use of low level spells pointless against casters of 8th level or higher.
If I were to hazard a guess with that data, I would think that doing makes no major difference overall when staying true to the SIEGE roll and that splitting it would negate a sizable degree of challenge when facing other spell casters, if not reducing the effectiveness of spell casters as a whole. Entirely supposition however.
1) Yes a 10th lvl vs a 10th level is head to head with even chances.
2) I like or have thought about adding extra negatives based on higher level spells... but that makes saving from spells hard.. if we did that there might need to be a "casting to hit" with penalties associated with higher level spells? But this is all off the books.
I think saves in general add level of the guy saving against the thing/guy doing the action against you.. good and bad come with this. A high level assassin make a poison from say a specific plant. you save against the assassin's level.. not the specific poison. A high level mage casts a fire ball doing more dice of damage than a low level mage and the chance to save for half is harder too! Logical to me in the second example but not the first.