Can a portal be selective? E.g. Can you set it up that only living things will go through it. Send in armoured cavalry, and get naked men riding bareback on the other side, while the back side of the entrance portal accumulates inventory?
Can a portal be made so that it only functions one way? If the entrance is very high, and the portal isn't charged, then in effect it's one way.
Can a portal be charged from either end, or is one end a master to the other? This can prevent a one way portal from being charged at the downhill end to allow infiltration 'uphill'.
Do both ends of a portal have to be the same size? What happens to a person who walks through a 6' portal if the other end is 4". Extruded like toothpaste? Are there other properties that come up from mismatched end sizes? E.g. is a big to small portal pair in effect a nozzle, with the exit speed multiplied by the relative area?
Tune it specific metals, place one end in the ocean in a current, and harvest gold. Or salt. Could you use this to get pure water from otherwise undrinkable sources?
One issue would be that for sparse materials (gold in seawater) the material coming through would be a gas. You may want the exit ring to be fastened to the neck of a large jar. Or you start off with a sample of the material, and it is flush to the portal, and the material plates out on the sample. It would act very much like vacuum depositing without the vacuum. Later on they could make integrated circuits this way.
Make a tiny portal. Surgically implant it in a person you want to control, or give a pill that disolves in the stomach releasing some mechanism that prevents it passing through. You can pass strychnine through the portal any time. Tiny doses will show him how painful the death can be.
Variations on a spell:
Can you make a portal that only passes light? This would be a magic viewing glass. Consider a gift of a partially silvered mirror with a lightportal on the back side. From the front it looks like a mirror. From the back you see what's in front. Make these up into spectacles. Wearers would be, "The Eyes of the King" Similar ones, bi-directional worn near the ear would be communicators.
If it's 2 way, and built into a pair of crystal balls, you have in effect reinvented Tolkien's palantir.
Can a light portal 'remember' and fast forward? In effect be a video recorder than can only playback once, as it lets the light it received back out in the same order.
Can a simpler light portal just delay light. Hold a 2" light portal up to the sun all day, and have an all night torch?
Can a light portal discharge all of it's light in a single flash? Take a 1 foot light portal, fill it with sunlight all day, keeping it oriented so that the light is always at right angles to the portal. Discharge all at once. This is in effect badly collimated 1 shot war laser. (it would spread at an angle of 1/2 degree) If nothing else this should be sufficient to set a ship's sails on fire from a distance, or temporarily blind an enemy.
Can a portal entrance be passed through a portal. If portals can be made elliptical then one can be passed through another. If you can quickly change the pairing between entrance and exit portal you have a method than an army can travel as fast as a team can run carrying the portal. You run forward until you are exhausted. Set the portal up. Next carry team comes through carrying a portal and goes another mile, sets it up. Meanwhile the end portal of the chain is tuned to the first set up portal, and everyone at the end comes through to the beginning. The end portal is then carried through to the beginning of the line. I think it takes a minimum of 4 to make it work. There are constraints on the relationship between the time you can carry fast, and the time it takes to pass an army through a portal. Probably better to have just the running team., and one more portal from the entrance to the exit at the end.
E.g. a 4 team relay.
Portal D is matched to Portal A.
A team sets out and goes a mile at good pace. Stops sets up portal. B team comes from start through portal D, carrying portal B and carries on. A team is reasting. Portal D is retuned to B. C team passes through D and keeps running. B and A are both resting. D team immediately picks up their portal and runs it to A, which now is tuned to ... The logistics of doing this get messy. You end up with 2 sets of of sprints leap frogging. You would need a set of interlinked communication portals to make it work.
Because of the gravitational/atmosphere equilibrium you don't end up with a hurricane blowing from a sea level portal to an alpine one. But normal storms coming through produce a typical variance of a few percent. If your end has a low in place while the other end has a high, you will have a strong headwind.
This might be commercialized with small portals. You have a farm of them in a part of the world that is chronically low pressure. The other end then is a good vacuum cleaner. If the size differential can be turned into a speed or pressure differential, then you can get better suction.