I like this idea. But you shouldn't be able to close the thing, and it should be invisible - but still accessible - to foreign ships(should they accidentally stumble upon an entrance). Instead of you closing it, it should randomly close in a few weeks with you having no control over this, but this closure will allow you to re-establish a new wormhole whenever you want without building anything more. Any ships inside will get randomly kicked out of either end with 1 hp and 0 movement points left when the wormhole 'decides' to close.
I think you should be able to close it. but in a different way. Basically, to build a wormhole generator you equip a ship with a wormhole generation module (which cost a sh*tload and take up a sh*tload of space). Then you move the ship where you want the wormhole to start and hit a button that says "generate wormhole". then you place the other end of the wormhole where you want it. The only way to destroy a wormhole created is to turn off the wormhole generator (which takes 5 weeks). But, turning off the generator should come at a serious price. If you turn it off, everything within 15 parsecs/spaces will get sucked in, including the generator. And once you collapse a wormhole, you can't place a wormhole whithin 20 parsecs of the original because of space time damage.
Also, this Galactic Achievement that you must build to create a wormhole should have a giant maintainance cost, based on how far the two ends of the wormhole from each other: it can be much higher for a longer wormhole. The longer this thing stays open, the higher the maintainance cost per week become, exponentially rising, just as prices get prohibitively high for spies. But the upside: Terror Stars should be able to access these wormholes. However, trade routes wouldn't gain any income for passing through wormholes.
I think that the wormhole generation tech (which would cost a sh*tload) is enough and no unneeded improvements or maintenence that rises in price should be used. It should just be a flat maintenence cost of lets say 50bc a week.