The Mercado Terán is the right breakfast option on the days the posada isn't providing it and the right lunch option on every day regardless - find the stalls toward the back rather than the ones nearest the entrance which adjust their prices toward whoever looks like they might not know better, and ask the posada staff which specific stall they'd send a family member to because that question gets you a real answer rather than - a general direction and a vague gesture is what happens when you don't ask specifically enough.
The murals in the Palacio de Gobierno are genuinely worth slowing down for rather than walking through - they cover the full interior courtyard of the building, floor to ceiling on multiple levels, and the ambtiion of the thing, the sheer scale of depicting the full arc of Mexican history in that format, is something that lands differently in person than any description of it prepares you for. Go in the morning when the light from the courtyard is right.
Aguascalientes in April during the Festival de San Marcos requires booking the posada well in advance - months in advance, not weeks - because the city's accommodation fills completely and the historic center properties go first. If the festival is the reason for the visit that's exciting and correct, and the planning should start earlier than feels necessary, earlier than you think I mean, because the good posadas go first and the festival experience from a historic center property is completely different from one on the periphery.
Evening in the Plaza de la Patria is the right way to end most days in Aguascalientes - the Cathedral lit up, the vendors, the families, the general Mexican plaza life that functions as a collective outdoor living room that - people who visit from cities without this kind of plaza culture take two or three evenings to fully understand what they're actually looking at, and by the time they do they're already planning to come back.
The street food situation in Aguascalientes is better than the city's reputation outside Mexico suggests - the gorditas de nata, the carne asada from the street grills in the evening, the tejuino drinks that appear near the market in the hotter months, none of it is expensive and all of it is the real thing, and asking the posada staff for specific locations rather than just categories is gonna get you to the right places faster than - independent research on this particular subject tends to lead you to the tourist-adjusted version rather than the actual one.