The engineer requirements are such that it doesn't appear that you can get ahead of the curve, and the nexus is much more expensive (300 cash + 130 in materials). Sure, I guess you save a base slot and 2 power, but other that it just doesn't seem worth it to go for bigger and fancier.
I didn't make one in my Classic run..a fringe benefit of losing a couple countries meant that my 2x2 block of uplinks was enough for almost full coverage anyway. I did eventually get a fifth uplink..could've removed one of the uplinks and built a nexus instead but at that stage in the game its pointless
You definitely don't need them and I don't think saving space matters..I wasted some slots and only used three floors..had to remove a lab to build the Gollop Chamber but that was just spring cleaning
I've been using stations on C/I, no problems so far.
The massive extra cost means that I can't imagine using them for a rush strategy unless you scum council missions for engineers and use the abductions for cash. Maybe if you sold alloys/elerium like crazy and delayed production of firestorms?
They strike me as more efficient as a long-term investment, but the short game is where you live and die.
On classic I think the Nexus saved me actually because, well, okay so basically each Uplink gives you +3 after the first one since you're obviously going to link all of them one way or another, and each Nexus is going to give you +5 since it's also able to link up with your Uplinks and not just another Nexus. By the time I could actually make a Nexus, I happened to need exactly +5 satellites for full coverage. Building more than one Nexus is kind of silly though because you do NOT need the extra space even if you're spamming Workshops like there's no tomorrow (Yes, I am aware that there really is no tomorrow if da Aliums win.) and it wastes time because you first need to build the Nexus for the redundant coverage that keeps your satellites going, then you can tear down your old Uplinks, THEN you can rebuild there. It's just a dang waste when a small cluster of Uplinks plus one Nexus will give you the same coverage in less time.
As for the greater cost of a Nexus, that just means I save more money from all my Workshop bonuses. And ultimately I feel like it saves you time.
Is there something about the way I type that makes it sound angry? Maybe it's just something about the way you read.
If you're trying to get a 16 country playthrough (possible, though not easy), you'll need Nexuses, if for no other reason to save space and excavation costs. 2 Nexi and 2 Uplinks in a square will give you exactly 16.