Doubloons are great. Some are very powerful and can make battles much easier. But some doubloons are limited in their usefulness. The main examples of this type of doubloon are the retreat ones and the maelstrom ones.
The retreat line of doubloons heal everyone on your team for a small amount each turn, as long as you don't do anything. While this sounds good, having to not give any orders is is more of a disadvantage than what you get back from the healing. These ones are easy to get rid of though, just use them and ignore the effect.
The maelstrom line of doubloons reduce all enemies accuracy by %50 and push them back. I can see how this might be useful, but it most cases it is just annoying. The push back interferes with targeting, causing many of your units to be unable to attack. Getting rid of these ones are tricky because of this.

Those are the worst offenders. There are others that are "useless" in minor ways. Like the summoning doubloons, which can summon into a place where your unit is moving. Or the Jackrabbit Ju-ju, which is awesome in the way it gives bonus epic talents, but it also gives %50 extra movement that can never be used because it it comes on after you give orders and wears out before you give orders in the next turn.

I would agree with Esperanza here: there are no useless doubloons. As they begin operation before the round officially starts, they all can be useful to everyone -some very useful. Like anything else, doubloons are best when used wisely.

'Retreat' is always good when things get tough and you and your companions are low on health. Even a little bit of healing can help. And if you or they are frozen and can't attack, or have an option not to attack, then the healing is more effective.

Maelstrom/Galewind etc. can nix planned attacks. It's happened often to me. But it is very effective when you have musketeers in your lineup (or Carcarius) who will fire at an approaching enemy; or perhaps knock your enemy into some bombs or traps they missed before! It will also give those using 'repel boarders' another chance to use that skill. Additionally, with really tough foes, like those terror-cota warriors (what a great pun!), pushing them back gives you a breather: they might not all be able to attack you that round!

Great juju is incredibly useful. It is great for the toughest fights. True, it can cause a swashbuckler to pop out of hiding before they can use one of their big attacks, but you get a bunch of other attacks during that round which will largely make up for it. The fact that everyone else also gets multiple attacks makes up for losing an assassin's strike.

And then there are doubloons like the shields, increasing agility, will, etc. that are always welcome. And those 'will' doubloons are not only useful for witchdoctor spells, but also seem to increase any healing done that round.