I think if something is cleared up for you then your task here will become substantially less difficult and you will then be able to find what it is you are looking for without the stress of being concerned with this issue you are concerned with, namely backwards compatibility. Newer versions are expansions of previous versions, they are not so much replacements. (There is a quote following that will back this statement up.) The exception to this has been the mobile devices which have specs for Embedded Systems, OpenGL ES 2.0 has created a division between the two. Desktop GPU manufacturers have not done this and likely will not do this.
Your concern is that open source examples are using "out-dated OpenGL" and that you cannot use them for OpenGL 4.0. The vast majority of the features in these old example are still a part of the newer spec. You are very unlikely to find any OpenGL 4.0 point sprite examples because the manufactures have already released examples on how to use these features. Nothing has changed, the old examples are still valid. OpenGL has been almost fully backwards compatible for 15 years now and that has not changed very much. This has always been one of the OpenGL API's design goals.
The idea that a feature becomes slow and obsolete because it has been around for a long time is a false notion. Many "older" features are updated silently behind the scenes through driver optimizations and new circuit designs that increase efficiency.
The following is a passage written by long time nVidia software designer Mark J. Kilgard. He has written more on the subject of OpenGL than just about anybody on the scene and does so on behalf of one of the biggest names in gaming hardware. What he's says here does not just apply to immediate mode rendering.
... the notion that an OpenGL application is "wrong" to ever use immediate mode is overzealous. The OpenGL 3.0 specification has even gone so far as to mark immediate mode in OpenGL for "deprecation" (whatever that means!); such extremism is counter-productive and foolish. The right way to encourage good API usage isn't to try to deprecate or ban API usage, but rather educate developers about the right API usage for particular situations. http://www.slideshare.net/Mark_Kilgard/using-vertex-bufferobjectswell
Consider it pure joy, my brothers and sisters, whenever you face trials of many kinds, 3 because you know that the testing of your faith produces perseverance. 4 Let perseverance finish its work so that you may be mature and complete, not lacking anything.