The Home Brew Audio motto is "knowledge trumps gear." With the right understanding you can make professional sounding recordings with very modest and inexpensive gear.
But the converse is also true. It is not only possible, but very common for people lacking the right knowledge to make poor recordings even with the most expensive gear.
However, I don't believe that the required knowledge has to be hard to understand. I try to make these audio concepts so easy to understand that anybody can put them to use, not just the techies out there. Check out some free videos from The Newbies Guide To Audio Recording Awesomeness to see what I mean.
I do think that if you plan to go into business as a recording engineer, daily recording clients with different needs and genres, you should have a lot more technical knowledge. That's primarily because the sheer number of problems you'll have to solve will be much greater than if just recording yourself.
And if you don't know how to solve these problems quickly, you aren't likely to remain in business as an engineer very long.
The following article lists 10 technical audio and acoustic concepts that engineers should understand. And since I believe knowledge is never wasted, you will benefit from reading through these even if you don't plan to become a full-time recording engineer.
The first of the concepts is the understanding of the speed of sound. I actually just wrote an article about that - Felix Broke The Sound Barrier In His Sky Dive – But What Does That Mean? - just after Felix Baumgartner's sky dive.
Check out the rest of the list here.