better solution: ditch level up bonuses so people don't have to worry about these sorts of things.
if you want cities to be able to specialise as they level up, assign these specialisations to buildings that require a certain level (and that you can only choose one of from a selection). that way players can do the specialising as and when they choose, and all the info is contained in one place: the buildings list.
level up bonuses are a clunky, half hearted way to make people care about levelling up. it smacks far too much of the "+arbitrary unexplained percentage" nonsense that we had too much of in gal civ 2. we have buildings, levels, and soon we're getting specialist slots as well. why keep an underdeveloped, tacked on mechanic that can be managed much better by the other systems?