Since I feel slightly guilty for not trying to help out on your original question (for what my opinion is worth...), I'll try this one.
Firstly, congratualtions on the second in-situ bromination method, what an excellent idea! Just make sure to use enough GAA to dissolve the liberated HBr (I notice sometimes that some sneaks out towards the end). Also, when doing the bromination on ring-methoxy propiophenones, I tend to keep the temperature at 0oC rather than 15-25oC; when brominating 4-methoxypropiophenone without cooling, the solution turned black and the yield was lower than usual. I think this is because the liberated bromide ion is poorly solvated in GAA, making it a better nucleophile and more likely to cause demethylation.
I don't think potassium carbonate will cause too much damage to the bromoketone. Since it isn't a nucleophilic base like hydroxide, there won't be a tendancy for nucleophilic substitution, meaning less decomposition. A bee friend of mine washes his bromoketones with potassium carbonate during workup, so it can't be too unhealthy, although I stick to sodium bicarbonate. NaOH does an excellent job of destroying bromoketones and I suppose gives the appropriate hydroxy-ketone in a rather exothermic reaction.
Also, a patent which may come in useful for those who don't like working with bromoketones and want to aminate the propiophenone as is; the catch is the reaction of an amine with bromine. Make sure to keep the temperature low! The method is patented by Kamlet, but no yields are given: Patent US2155194 (http://l2.espacenet.com/dips/viewer?PN=US2155194&CY=gb&LG=en&DB=EPD)
. This could be a nice route to consider if we could find another suitable source of N+ instead of using toxic haloamines.