Since the issue is near and dear to my heart, I'll hang on to all that expended brain sweat. =)
Flat attribute boosts would be a Bad Idea™ because they annihilate the need for soldier experience.
What is a much better approach is to let an armour give a % increase to a stat.
A 130% strength armour is not going to turn a 30 strength soldier into the Hulk. It only goes up to 39.
This way a heavy suit of armour can let a soldier use very heavy weapons that unaugmented soldiers can't use or can't use very well.
For the really good stuff you still need a naturally strong soldier, though, so soldier experience always stays valuable.