Spying?

You have to place your spies on a structure, the more you place, the faster you get intel. 

any secret to keeping them alive? They almost always get nullified in one turn

This seems incorrect - in all my games of TOA, you can do exactly what's described in the OP: place race-wide agents to get intel.

The 'trick' there is that your enemy needs to be under enough pressure to make keeping a healthy pool of spies impossible. If your economy is far superior, you can probably spend your way through decimating their store of spies and stay ahead in producing new ones. Getting them involved in a war with someone else can also help.

I tend to stockpile spies until I'm very serious about a war, and then I try to blanket every econ building I can find. Even if I lose a bunch from that first wave, as long as a good number make it through, the enemy will have a harder time paying for new spies. 

Yeah I also use them on morale structures when invading so I can invade using propaganda (can't recall what the warefare type is called off-hand)

I guess somewhere between the original ToA release and the most recent patch they added back in the race spying UI I remember from DA. Now that I have the most recent patch the spying interface is similar to the previous Galciv2 releases.

I can't get techs by spying. How do I do that

How do you spy? You can not get techs by sabotaching planetary improvement. You need an advanced espionage level on the civ you want to steal techs from, and theb be patient and a bit lucky, and your spies will steal techs eventually.

As I see I don't need keep my spies on a civ. So I can reach advanced level on every civs with 4 spies only.

Until I have ADVANCED level on a civ I can't see their starbase details. If I double click on one of their starbase, I get a message about that. However if I only select the starbase and then click on info button, the detail window opens. This may be a glitch, I think.