I've found an odd random assortment of banners, myself. I've seen as many as ten available on a single station. The fines and rep hit are a fair point, but I wonder if that might not actually further synergize with donation missions? Those give my power, at least, about a dozen merits per mission.
It helps, certainly, though you'd have to get very lucky with the mission board to still not be losing net rep with the station owner at a high-banner station.
(Big expanded BGS factions + Power bonus to rep gain in friendly space gives you a bit of chance to also throw donation missions at the other end of the trade loop, of course)
I don't think hacking needs to pay more merits than it does, certainly - though the rep hit could probably be toned down without making it anywhere near overpowered.
Actually my main feeling is that most of it actually feels pretty well balanced already. I have a whole range of activities which can get (singly or in sensible combinations) about 3k/hour, or would do if I was better at them. High-profit local trading needs a rebalance for the 1t issue, the data bug needs fixing, crime is a bigger issue but in the short-term it should pay more, and they need to decide if they're dividing rares by three or tripling everything else ... but other than that I think it's mostly there in terms of the balance between activities and activity groups.