I found a way to enable additional services, given the lack of options shown for you (and me) on the Google Apps/Add Services/Other Services page.
In my case, it is the actual Google+ service that I wish to enable.
From the Admin console, I clicked "Users". Then I clicked on the name of one of my main users to view their User Details. Then I clicked "Show More" at the bottom of the page, and one of the revealed headings is "64 More Google services enabled". I clicked this and a side-panel opens up, with a list of services.
Scrolling through that list, I noticed that Google+ was "Off". Clicking on it took me to a page with a large g+ icon and a drop-down underneath that allows me to select "ON for everyone". Clicking this brings up a confirmation dialog that warns that it may take 24 hours to take effect, so I have yet to confirm that this works completely.
Hopefully this might help with the Picasa service, which I see is also in that list of "more services", albeit already ON for me.