Your assumptions are all good except for reciprocity failure, but that won't be an issue unless your exposures are several seconds long; absolutely not relevant in your daylight situation. It'd only matter if the ND changed a 1 minute exposure into an 8 minute exposure or something like that.
One stop of overexposure on Delta3200 is absolutely not going to hurt anything. In fact, the usual recommendation around APUG seems to be to shoot at 1600 and follow the development instructions for 3200. If it's any other negative film, it'll still be fine with an extra stop.