Here's what I have so far in my work on analyzing the strengths of all items. This is a work in progress and I'd love any feedback or input that anyone has on it, or what kind of deeper analysis you might like to see (either mathematical or "practical").
I'm warning you now that the attached spreadsheet is extremely ugly, and has an immense amount of information on it which you probably won't want or need. Here is what you should know if you venture to try to read it:
I included both the Starting and Maxed value of various items, and separate listings for the value of some aura-items for yourself vs for those around you.
The "Base Gold Per Stat" is derived from the gold cost of the basic items that provide that stat.
The Stat/100g columns are how much of that stat you get per 100 gold spent on the item. It's useful if you are looking to stack that item as efficiently as possible to the EXCLUSION of all other stats. (generally, the base items are best for this, as they waste nothing on other stats)
Near the right side, there is a set of "Cost" columns - this includes the total cost of the item, the gold value of the base stats it provides, and the "cost" (the difference between those previous two) of any advanced stats, passives, and actives. I used Penetrations, Dodge, CDR, and Movespeed as the advanced stats, since you can't buy those without other things attached.
"My Analysis" at the very far right includes how I interpreted the numbers I got, and a few calculations regarding how cost effective various passives are like "2% of your health as damage" or whatever.
It may be useful to sort these items by the various columns.