I think people deserve a second chance. If you like everything else about that person, and the spark never appears, then you might have made a good friend of the opposite sex.
it's tricky. For me it isn't about wasting time really, but more about creating expectations to the other person, ending up hurting them. It is of course up to them to handle it but you know, i'm thinking about it. Still i'd go.
SW-User
If you had a good time the first date, spark or no, then why not?