I don't know if I'd just write it off like that . Musicals tend to deal a lot with characters' emotions and personal issues, so I wouldn't be surprised if we got some fairly significant developments in The Flash episode. Just look how important Once More, With Feeling was to Buffy's story arc.
Once More with Feeling is a huge exception, in my opinion its the only good non-animated musical. But, I think Flash's will be more like the second of the two unwatchable musicals Xena had (specifically Lyre, Lyre Hearts on Fire). That was just a bunch of badly done licensed songs in an episode that had no point and with a stupid story on top of that. That seems like the kind of musical Flash will have, except it might mention some elements of ongoing plots. Besides, I imagine they know they'll have a chunk of their audience tuning out for the musical, so nothing big will happen. Even Buffy didn't put any story changing things in the episode, just a few revelations about character relationships, and Flash doesn't have any stuff like that at the moment.
Whatever. Disagreeing with you doesn't make my opinions "hyperboyle". But like I said, the musical is, in the end, irrelevant. Its just a waste of time, but we'll still get normal Flash episodes after that. A one week interruption to programming is unfortunate, but easily forgotten after its happened. Its annoying and pointless, but not something to get too worked up about, except maybe about the missed opportunity of wasting an episode. I'm excited for the rest of the real Flash episodes this season, and I'm personally not going to make one horrible, but in the end unimportant, mistake bring my excitement for the show down