I went and saw the Bayside/Saves the Day tour the other night and it got me thinking a lot about longevity. How did those two bands last so much through one of the most progressive times in the music industry? How did they survive against the elements of death, label issues and pleasing longtime fans? Hit the replies and let's talk about not what makes a hold any sort of longevity past "putting out good music." What makes you continue to see your favorite bands year after year or multiple times a year at that?
Bayside managed to progress without progressing. By that I mean even though they're sound has gotten crisper and more mature, the bands sound has changed very little. They consistently put out great records with catchy hooks, I can't think of a single bayside song that I don't like and that helps too. Saves the Day on the other hand was such a big name in the genre that everyone has at least one STD song that brings them back to the good old days (similar to TBS, Blink, NFG, or BN). It's the emotional connection to the band that keeps long time fans at least curious to hear new music.
"Saves the Day" as a band is more or less only Chris, so I think the dynamics there are different than a band like Bayside (with who, admittedly, I'm not overly familiar).
Saves the Day released their seminal albums when the 'scene' was burgeoning and gained quite a few followers who have continued to go to STD the shows over the years. Combine that with older people saying to new kids, "Hey if you're in to ___________ 2011 emo/pop punk band, check out old Saves the Day" and those kids going to shows. I don't think there's much more to it than that.
at the end of the day, longevity comes from connecting to your fans in a way that induces nostalgia. people have to associate your music with either a good time in their past or a difficult time that your music helped them get past. in my opinion, that's why blink 182 got so huge in the first place and was still able to catch people's interest when they released an album after an 8-year break. Of course, there is no set formula for accomplishing this, and it's pretty easy to tell when bands are try to manufacture nostalgia vs. being naturally nostalgic.