These 2 phrases:
"Instead of the free sharing of ideas...I'm encountering more and more the attitude of a guarded sharing...the real knowledge and experience seems to be held back because it...might be used to turn a profit somewhere"
and
"Todays big topics leave me pretty much unenthused"
I hear a lack of motivation, not for technology, but for the specific purposes to which technology is being put- squeezing a buck out of things.
But you're mistaking the impact that incentive structure has on your motivation for a lack of motivation about the technology itself. It doesn't work that way.
I suggest finding a way to spend time with organizations that have a different incentive structure. Find someone you know and talk to them about how they use technology. It wasn't entirely deliberate, but looking back, I can say I found a way forward when I started working with non-profits and helping at schools.
It takes a little while, but being around people who have a non-financial mission, and then being able to deploy what are still in those areas incredibly useful and rare technical skills- this feeds the motivation engine.
Making money is really important, and it's very visible; the context in which the work happens is invisible, but it's even more important.
So- it may take some time and thinking, but I would advise- stop thinking about the details of the sausage. Server side, client side, mobile, whatever- it's all just sausage.
Think about purpose and incentive structures.
The note you wrote is evidence that this matters to you, and that, like a vitamin deficiency, you're missing the motivation that comes from a different sort of incentive structure.
I would also respectfully disagree about the open source revolution being over. For technical, social, economic reasons, looking at the trend lines, it is very far from over. Open source, free software- this lives in and feeds an ecosystem that is not about making a buck, and there are healthy and growing areas in which these incentives are dominant. That OSS and FS can be consumed by other ecosystems- that's fine, the world as a whole is healthier when you have a balance of both. This is precisely why FS licenses are written as they are- the act of creating a tool to a certain degree has to be agnostic about the uses to which the tool will be put. But OSS and FS are still growing, and gifts are everywhere being created.
Good luck.