I think the TNG film series was a failure, and it's to be expected. There was a huge amount of inbreeding going on, and unlike with the TOS films, which tried to put the series in the hands of new blood, Braga, Berman, and Moore were continually put in charge.
Gen was terrible. The TOS portions were obviously written by people with no respect for the characters, and every single plot point is ludicrous.
FC is supposed to be a huge success, but no matter what you think of it (I hate it) having to retool the series to make it action oriented and turning the concept of the Borg on its head in order to get people's attention is not making a successful *TNG* movie.
INS was just dull. It comes closest to an episode of the show, but a bad one. Despite the fact that FC did well, INS seems to have been screwed on budget.
NEM, I don't think there's any question here that this is the worst of all Trek films. TFF is more watchable.
So, yes, the TNG film series was a failure. AGT would have been the best goodbye for the series.
THIS!
As far as the cost of TMP, Paramount wrote off all the costs of the aborted second TV series against it.