Suggestion: Micro-rifts

[Canicus]

Micro Rifts are pretty OP, no upkeep and instant travel around the map.

Possibly they should come with a penalty like attracting creeper, causing more creeper to spawn and if the creeper reaches a rift it will take damage but the creeper would also flow out from the other rifts.

Still OP but with great risk comes g great rewards.

[Sorrontis]

Well they are end-game units that cost 400 redon to start the initial connection (200 per gate). They also need to be made in an area you control.

[Grabz]

Do share some of your best leaderboard scores where you've made extensive use of MRifts, I'd be really curious to see some good times using them, if they are so OP and all :)

[Feralprowler]

Canicus:
Micro Rifts are a callback to Creeper World 2. I was pleasantly surprised to find them in here. In that version, I do not believe that the creeper itself could flow through the rifts, but certain enemy drone units could. It would be interesting to see some of the mobile units being able to slip through them here. 
Sorrontis:
I agree with your assessment. They are easily the most expensive Redon unit in the game. Redon is usually the resource that is generated the least, and considering you need it to fuel some other things (such as the missiles) you cant really build many of the rifts simultaneously without potentially depleting your redon intake.

Canicus:
I don't feel they are particularly OP. All they do is shorten the packet travel time, though of course they do provide a gate if part of your network is destroyed. I feel the expense and long build time of the rifts, is to ensure that if you are putting it somewhere, its somewhere you already have very well secured, so it kind of defeats the abuse potential of say, building a quick line of towers without securing them, jus so you can put a rift somewhere.
In CW 3 you often had 2 or 3 different command centers you could use, so you could have multiple points. You also had the ability to increase packet speeds. With those taken out, I feel the micro rifts help emulate that.

Ultimately, I feel the Micro Rifts are a well-balanced addition to the game, though I do think it would be interesting to see enemy units being able to move through them. Having creeper move through them is pointless though in my opinion.