Blue gate
So, there's this gate with not even 1 full ring and only two? days left:
http://wiki.spiralknights.com/images/6/66/Ohrats.jpg
Should we spend all our minerals on it, or will we not be able to finish it in the remaining days?
I'm afraid we get another situation like the silver phantom one in the next days.
Well, if we all do party runs then we should have about 40 to 50ish mineral each.... Should at least get it to emberlight if we do non-stop full party runs for a while.

How can one tell if a gate is full?
What's wrong with a small gate?
(Seriously; I'm too new to know what's wrong.)

We only get N gates open at the same time. If one of them doesn't go all the way to the core, there are less levels to choose from at a time, especially if you are in a town below Haven. If no open gates go deep enough, it may not be possible to play from the lower towns at all, which means that people have to go back up to Haven and whomp stomple little baddies with their high level weapons, which is less fun.
A gate will not have the maximum number of floors if it is not filled completely. That can mean no floors past Emberlight, which means that we'd lose our main source of materials.
This is a problem that was likely caused by both the variation in gate timers (which has hopefully been fixed) and peoples' poor understanding of the mineral system.
Most people seem to just dump all their minerals into the leftmost gate. This is usually fine except they still do this even when another gate will open earlier, or if the leftmost gate is already full.
I think there needs to be more information given to the player about how they should be using their minerals. The NPCs tasked with explaining the system don't do a very good job.