I can only speak for myself but I see no need for over dramatising the need for social network optimisation.
I worked as an SEO & SEM consultant for over 10 years, preached what the market said was the in-thing and earnt well doing it.
Now, I mainly run my own sites and you know what - I don't use Facebook, Twitter or the rest - all of my sites are placed in the top 5 in their niche in Google and placed well in other search engines.
Clean, well thought through code and decent unique content is what has been and will always be the long term winner.
When it comes to MODX, well, the optimisation is down to you - you can set-up TV's per page for meta tags, on-page optimisation using relevant code semantics always helps (IMO).
A little off-topic:
Other factors could include:
Use a responsive layout to accomodate for the various end-user devices that are used in todays mobile internet
Page load speed must be taken into consideration
Image optimisation - including file size and relevant HTML tags
The list goes on and on