A way to make one Drupal site act like several sites I would like to create several sites each with same number of features (content types) but the ability to select different theme. 
If I go with multisite feature of Drupal I will have difficulty in setting up and managing all the sites. 

I can achieve different sites with Organic groups. But the spaces module is pretty much not working and needs serious development for 7.x version. I tried with all the patches but still it gives me a lot of trouble.

My requirements are more or less same as OpenScholar distribution but I would rather like to use Panopoly (panels) than boxes and context.
Also Openscholar has way too many features that I dont care of and exerts some serious load on the server.

Are there any alternatives to spaces module? Any help would be appreciated. a Case study perhaps.
Have you looked at the Domain Access project?