In mid September, we stayed for one night in Le Vieux Manoir on our way from Nice to Cherbourg. The hotel was great but unfortunately nearly every shop and some restaurants in Amboise were closed on Monday afternoon and the whole town felt really dead. I know it's really all about the Chateau, but we were surprised at how dead the whole town felt, given that it is a fairly well known tourist destination.
We also managed to eat in a terrible pasta restaurant beside the Chateau. The staff in the Touraine wine tasting centre and shop seemed bored and were rather unwelcoming.
We have been to Amboise before, in May, and it was fine. So this is just a warning not to go on a Monday unless the Chateau is all you are interested in!