As for the other ship designs that showed up in this discussion, I use them more often, as their use is subject to situational suitability.

Galleons, while being rarely used, are nonetheless useful. It just so happens that many players don't quite have an idea on how to use them. They can act as transports, scanning ships, minelayers, invasion ships, light warships, overcloakers... you name it. Ever wondered why the SS players out there insist on using Rogues? The Galleon gives (almost) the same flexibility, albeit in a bigger, clumsier package that is more expensive. One thing that helps designing Galleon-based ships: think about the purpose. You'll be throwing out quite a lot of minerals and resources - make sure you'll get the bang you wanted for this buck. The best scenario is when you can combine two or more functions in just one package and cut on design slots this way. That's what Inquisitor80 alludes to in his OP - in the light of this, I'm doubly amazed that he doesn't find any serious use for Galleons

As for the "dust-biters" (as I call the remote mining ships) - the idea is simple. Either you have OBRM and pretty much forget them, or you're ARM and you stick to the ARM-granted hulls and robots. That leaves the other "intermediate" hulls and robots largely ignored. Still, if you're neither ARM or OBRM, you can still benefit from RM - sometimes you end up with all green planets having poor concentrations of the most wanted mineral (usually Iron or Germ), and you have to make do with mining fleets. Even if you're OBRM, sometimes you may be forced to pay the hefty cost up front, just to get the minerals you so badly need. After all, are your 1320 mines@1,3kT/y capacity of any use on a planet with all mineral concentrations reduced to 1 by years of wanton excavation?
For me, the decision on using "dust-biters" is simple. If I need them (i.e. have good MCs on reds nearby, and poor MCs on my greens), I go for them, and then I use the best hull/robot combo available at the time. If not - I don't.

Lastly, expanding on iloverushandledzepp's comment on Colony Ships - you don't need more than one pod per fleet to colonize a planet. Also, if you give Colonize order to a fleet, all ships in that fleet get dismantled for colonization purposes.
For this reason, it pays to keep the good ole' Santa Maria in your design list for longer time (especially if you took IFE and your colonizers are Mizer-equipped). They pack a surprisingly long range, and you can send them together with another fleet of transports (with extra colonists/minerals). You can then give the Colonize order for the colonizer only, and have the other ships simply drop whatever they brought, and return for more. You don't pay an awful lot for a small colonizer, and the rest of the ships can be reused. About the only purpose of having more colony pods per fleet is when you play an AR race - their Orbital Construction Modules double up as bombing pods capable of killing up to 2000 enemy colonists per pod (modified by standard defences cover