How about leaving stat gains and most things alone, and just scale down how increased stats affect a creature's strength? This would then fix tokens as well, while doing no harm to people who spent tons of effort to raise their stats.
For example:
If <total increase in a stat by tokens/influence/skillvampire> is not negative,
<creature's stat> = <creature's base stat> * ln (<stat increase> + e)
This way, even with a billion attack, you'd only multiply the creature's attack by 20. And with only 150 attack, it would be multiplied by 5.
There would be no limit to how high you could increase a creature's attack, but the effect of further training your stats would be absolutely miniscule at the high end.
With 0 stat increase, the stat would stay as it is.
Logarithms are very simple and useful.
You could use a similar equation for negative stat increases, just making sure that the two halves of the piecewise function are continuous at 0.
EDIT: Woot, 500th post.
EDIT2: I just realized that this type of change would make creature initiative matter again. For example, a newbie's aramor would always attack before a veteran's grasan.