Smaller / easier to carry, hide, use than the JB3: R-09.
Budget of $200-400: R-09 or mics.
Improve sound quality: R-09 or mics.
Based on the above, I agree with some of my fellow TSers. R-09 is the way to go for the moment, as it fits all three points - usability, budget, improved quality. Upgrading your mics will also have a positive impact on sound quality - perhaps more significant than switching to an R-09 - but usability will still be an issue, and the JB3 will still limit the quality to a degree, as well.
Stack taping = standing very close to the PA stack and recording as much direct signal as possible while minimizing the sound of the room
Ambient recording = standing farther back in the room, preferably in the "sweet spot" where it sounds best
The reason I asked about stack v. ambient: omnis are quite good for stack taping, but sometimes suffer for ambient recording due to crowd noise, poor venue acoustics, less than ideal location, etc. (That said, they can really sound great for ambient recording in the right crowd / venue / location.) Cardioids, on the other hand, can help mitigate crowd / venue acoustics / location challenges. So it might be worth considering a pair of stealth cardioid mics as a next step in the upgrade path.