We haven't seen any valid uses for having more than one of any types of those weapons. Anytime we've seen a build with anymore than one of the above weapons, it tends to fail miserably.
Regarding the double flare, having two left side flares on a pyramidion was, and to a lesser degree still is, a viable competitive build. In this configuration, the rearmost flare serves the utility role of illuminating enemy ships obscured in clouds, while the frontmost flare is used offensively, since before 1.3.2 (IIRC) two flares would put twenty stacks of fire on an unchemsprayed component (they now add only 16). This is even more useful since the flare requires very little attention from the pyra's main engineer to operate. Now, since the buffing of the banshee and flamethrower, there a number of other good options, so it sees less use as compared to before. But it's still definitely a viable setup in certain circumstances, and indeed saw heavy use by Captain Smollett of the Paddling (Icarus's most successful team from March to November of 2013, and arguably the most successful of the Icarus competitive scene to date).
Regarding mine builds, I have yet to see one succeed at the highest levels of competitive play. It is, however, an undoubtedly effective and entertaining way to clear a pub lobby. The sudden violence of one's ship being disintegrated by multiple mine hits is certainly one of the most frustrating ways to die, and has no doubt contributed to many a new player ending their nascent airship career in utter despair, as Gilder rightly claims. However, more experienced opponents with a ranged component to their strategy can quite easily avoid this fate by simply flying backwards and refusing to engage at the mine ship's optimal range. Mine junkers are particularly vulnerable to this tactic due to the difficulty with which they control their engagement distance, which is absolutely critical in mine combat. It's also why the most effective mine ship that has yet been seen in competitive play is the Squid, which can both control its engagement distance while at the same time bring other tools to the fight instead of relying primarily on mines, which is a strategic mistake. On the whole, reliance on mines is a risky strategy, with many potential counters and a relatively limited number of contexts in which it can truly succeed vs. a prepared and thoughtful opponent. Its greatest appeal comes from the fun and satisfaction derived from its use, not from any real competitive advantage.
(I should note, however, that this does change in CP maps, where they become much more viable due to increasingly claustrophobic engagements)
