Does anyone have more info on this event?
There are actually TWO events of this kind: a fast and a slow one. With a fast one the civ gets each turn an 1% increaase in many (if not all) "fields". The slow one gives 1% icrease in only one field per ~2 turns. Please note some of those fields are no more in use (like Crime, or Government). So nothing to worry about the slow one.
But the fast one... If the civ in question is significantly smaller than the big players, and it suits you to keep it alive, just watch it carefully. If it's a moderately sized one... In 50 turns they'll have 50% bonus to production, econ, reasearch, morale, weapons, defense, soldiering... Don't keep them alive, if you want a solo victory, because you'll not be the one who'll win.