I try not to see it as a company banking on nostalgia, but rather a testament to how successful and loved these franchises are, even after they finished a long time ago.
The people who want more are in the majority, and the people who say no are in the minority. And if the original creator and as much of the original cast as possible are willing to come back and giving us more, if they still have that creative drive and they've come up with more material after having some time to rest and do other things, then why not let it happen? In the case of DBZ (though, I apply this logic to anything), if what we get is something boring and lack luster, at least it's better than something that dishonors and destroys what we use to like about the show (in this case, DBGT).
I forget who explained this, but from what I understand about television practices in Japan, you have to really work hard to earn and keep a spot on TV. Ratings don't save a TV show as much as it does in other countries. You hardly hear that much of reruns, let alone new entries into a finished show. The fact that DBZ, Sailor Moon, Saint Seiya, Evangelion, and even popular Tokusatsu titles are having continuations made must really speak to just how popular they are. Japan has never really struck me as a country that tries to bank on nostalgia unless it really is a sound investment. And even then, they seem to be picky about how they do it. DBZ Kai cut the filler because they wanted to make the anime more like the manga, and the reason why people are happy Japan did that is because Akira Toriyama and TOEI, the creators, are the ones who know what to cut out and what to keep. They aren't half-guessing at it like FUNIMATION and SABAN use to do, and all because the Japanese execs were breathing down their throats and telling them to air the episodes as fast as possible and "just make them cool". It's kind of similar to how FMA Brotherhood was made. If the original anime hadn't been so successful and popular, I bet the Japanese company involved would have just let the property die out with the original series that ended differently than the manga did.
Besides, it's not like old things coming back is canceling out the creation of new things. If it really isn't for you, that's fine. Let the people who want it have their fun.