Hmm this quick reply thingy doesn't like the iPhone very much...
Anyway, I know its a rhetorical comment, but 300 checkboxes or 50 sliders is over-kill no matter what systems is used. The UI has to be something like 20 items (I'm thinking the custom race designer in MoO2 as an example) or people get bored with it.
Here's my idea for a compromise - a slider with 5 ticks. So using appearance as an example:
2 right is godlike beauty, +20% marriage / childbirth rates, +15% prestige. Costs 3TP
1 right is handsome / beautiful (change for diff sexes), +10% MArriage / child birth rate. Costs 1TP
center is normal looks, 0 talent point cost, no bonuses.
1 left is ugly, -10% marriage / child birth rate. +1 TP
2 left is part orc. -20% marriage / child birth, -10% prestige. +3 TP
You do that for appearance, grace (clumsy vs agile), constitution (hardy vs sickly), and a few others to determine the sovereign's basic attributes. Checkboxes are used to showcase special traits, like production bonuses, the spellpoint generation trait, etc. Maybe make it so certain checkboxes are greyed out when a requirement is not met - need handsome or better to be a charismatic recruiter.
This will do a few things - it breaks up sov design so it's not just a list of things to check, it shows what traits are exclusive, and it reduces some of the complexity of sliders.