Interesting. I have three IC-7000s, two of which are installed in mobiles. One is brand new, the other was the first one shipped by AES, and has been installed mobile for well over a year. I have never noticed the mic gain was low, and in fact, it is a little too hot even when set at 25%.
From my 35 years of mobile experience, most of the problems seen as low mic output levels has been a result of not using the microphone correctly. Electret element microphones require the user to "close talk" the mic, directly into the element. Talking across the element, or from distances over 4 inches or so, will greatly reduce their output.
The other side of the coin; increasing microphone gain also brings up the background noise, which is already a problem in most mobile installations. An average mobile is easily 30 to 40 dB louder than your average living room.
Adding great insult is the use of compression. I have never used it mobile, and have never found it necessary. The most important attribute any operator should strive for, especially in a mobile setting, is clean and clear audio. Adding gain is not the way to approach that end.
Personally, I wouldn't touch this mod.