Spire can be really useful for PLD. Not really answering your question about what DPS needs what, but thought I'd throw that in. This is only necessary in really long fights, though, or fights that need a lot of stunning (Shield Bash costs a nut and a half in TP).

As for Spear, the only DPS job that I can see truly benefitting in a very regular basis is SMN, since they have a whole load of OGCs that they use all the time and aren't fixed to a set rotation. If you have a fellow Scholar, it can help them too.