...as a numbers guy I would be happier if there was some sort of guideline for me to use. Not too specific, because I don't want my players to get so hung up on the numbers that they try to min/max the game...
Here is the guideline.
Let the players know, ideally during the Attribute Auction, that wimpy bids are likely to result in the specific Attribute being weak.
For example, from time to time I've pointed out that the Attribute Auction sets the 'ladder' for the player characters. Not for the non-player characters. If, for example, the auction for Endurance sputters out, then I might (and have, on many occassions) point out that the player characters might have some problems when they face off against, say, dwellers from the Courts of Chaos, or some other factions.
This perspective explains Corwin, and why, in Zelazny's books, Endurance is hugely important. Effectively, Corwin bid high on Endurance, higher even than the highest bids for other Attributes. Therefore, in Zelazny's version of Amber, Endurance ended up being the decisive Attribute over and over again.
Erick