I certainly understand your frustration but the problem, as you've adequately described above, really isn't the Kemper. When more humans fill the room, it's not going to affect just the guitar. It alters the entire mix. Even if they added the features you want for your amp, your singers, the drummer and even the bass player would still be screwed.
While the realities of low paying gigs is that people often can't afford to hire a sound man, doing a fire and forget soundcheck at the beginning of the night almost guarantees you're not going to be sounding great by the end of the night.
There are two problems to overcome when running sound from the stage. First, someone has to be available to turn the knobs in the first place, which isn't always easy in the middle of a set. Second, even if someone has time to tweak the sound, you're flying blind from the stage - you have to hear it from out in the room.
While there's no technology (Kemper or otherwise) that will solve these problems, there are options that might help. It's common now for digital mixers to have companion iPad apps. As an example, my Yamaha TF5 has an app called Stage Mix that brings up all mixer features on an iPad. You could mix an entire show just sitting at the bar with one of these things. I'm pretty sure there are other brands that do this sort of thing as well.
If you can't afford to hire a sound man, if you had a mobile app like this then maybe there's a song here and there where one of the band members could sit the number out, roam the room with the iPad, and adjust the sound according to the crowd. This would mean buying a mixer that supported these features, but to solve this problem you're going to have to spend money one way or the other.
Of course, the best solution would be for everyone in the band to take a bit less money and hire a professional sound man. If you can't make that happen, the only real solution is to find a way for someone to periodically get out in the room and adjust the sound accordingly.
