Just to add my little spin on it all...
Forget about collecting Obelisk data and Sentinel scrap at the two active Guardian sites.
I mean, sure, scoop up the debris from any Sentinels you destroy and scan any Obelisks you notice but don't worry about collecting specific amounts of anything.
Concentrate on activating the Guardian machine and collecting the BP fragments you need.
When you've got all the BP fragments you need, head to Col 173 Sector QU-O D6-25. Planet 5B.
It's got a Guardian Structure site and it's got 2 Guardian Ruins sites on it, all of which show up on your Nav HUD.
Go to the Guardian Structure site and it spawns a heap of Sentinels which you can actually have some fun blasting for the mat's.
You'll have to re-log but it's MUCH easier to get the required parts 'cos the Sentinels just spawn immediately when you enter the site.
Head over to one of the Ruins sites and scan the Obelisks there to get the data you need.
They're big sites with heaps of active Obelisks and you get 2x data from every scan.
Took me two nights of "play" at the 2 active sites to get about half the stuff I needed for all the Guardian items.
Thought I'd try the 3rd site just for a change of scenery and I got all the rest of the mat's and the data in about an hour.
Seriously, don't waste your time farming Sentinels and Obelisks at the 2 active Guardian sites.
It's cripplingly slow.
Get the BP fragments and then go to the 3rd site to get the mat's and the data.
Pretty sure that's the whole reason the 3rd site exists.
EDIT
Oh, and for "easy mode", go in a DBX with a Point Defence mounted somewhere on top.
You'll be able to land a DBX within the limits of the sites.
Then your PD will be able to shoot down all the missiles the Sentinels shoot at you while you laugh at them.
Commander Stealthie,
If you see this, please update your post to indicate that this site will be labeled Ancient Ruins [2], as the other one does not fit your description. Also, you indicate that you can get mats in addition to data, but I don't see any destructible panels, or mats laying around. Please clarify how those are obtained at this site as well.
Thanks,
Riôt