Rather than saying "half and half", I prefer to sectionalize my practice sessions and then time out each section.
My basic practice session has at least three sections: warmup, technique, and repertoire. My warmup rarely changes, thus it is a set and consistent amount of time in each session. Technique changes occasionally based on what I decide I want to work towards in my general playing. However, within consecutive practice sessions it is also going to be a consistent amount of time. I tend to blend the warmup and technique portions into one, so that my warmup is rather short, but by the time I'm done working on technique, I'm ready to play some repertoire at 100%. You may do this differently based on what time constraints you're working within.
If I am working on repertoire outside of my playing ability, then the technique segment is going to be geared towards developing that specific ability.
Repertoire may contain etudes, a solo work, or both, but I would strongly encourage regularly working on short etudes in tandem with solo repertoire as a way to develop reading ability and maintain general technique.
To recap, I'd say the most important part of improving your general playing ability per practice session is picking a single aspect of playing you want to improve over the next few weeks, work it into your regular, timed-out routine, and then execute it consistently every single practice session.
Even if the rest of the session is a horrible time reading etudes or solos, you'll still have gotten something useful out of your warmup. No matter what you do, just make sure it's the right thing at the right time, and then do it consistently.