Quick Note: Saving Throw Modifier over Straight Saving Throw

From my understand of the rules in Swords & Wizardry and a lot of other Retro-clones, A character has a straight Saving Throw (ST) that he or she must roll in order for something to happen (or not to happen). Sometimes their are situation modifiers that affect the ST but overall it is a straight number. So a level 1 Cleric has an ST of 14 while a level 10 Cleric has an ST of 5. These to roll targets represent appear to represent what the character may need in any situation. 

One thing I been thinking about (in that ever churning, unable to focus mind of mine) is in changing the straight ST to a modifier for my Eira setting. What this would mean then is that a level 1 cleric has a 0 ST modifier while a level 10 would have a +4 ST modifier (mod increase every 2 levels). So if, say, the Referee wants the Cleric to make a saving throw or be hit with the charm spell, the character would have to roll a d20, add the ST mod and see if it beats his or her Wisdom score.

Originally I was considering getting rid of saving throws altogether and making it just a meet or beat system. However, I thought that would be unfair to long living characters.

So, what thoughts are out there on this?