it is never a bad time if it fulfills your goals. Are you swapping a better town for a smaller house? More yard for less house etc.
So you are correct, if the market conditions in each town are comparable it makes no difference if the market is up or down ( keep in mind to budget between 5%-8% for all your fees, commission, tax stamps closing costs, moving fees ). So even if the home values are the same.. it's not REALLY an even swap.
Also consider that the market affects different towns differently... do you think Dorchester has fallen more or less than Hingham? It's not even close.. Dorchester has been slammed while Hingham is OK.
Quincy is where I live, and one of the town that I have constantly updated market information for, including hard to find info like all sold homes, list vs sell statistics and more. I work in Scituate as a buyer agent.. but do not catalog Scituate statistics.