At any responsible business with 100+ employees, third party software often passes through legal if it doesn't adhere to a pre-existing license(apache, mit, etc.). I think it wouldn't be correct to assume that there are only a few people concerned with licenses, especially because no license means all rights reserved, and you guys are pretty close to "no license". There are excellent licenses to choose from, and some already seem to fit your needs(as you describe them).

On another note, I personally see a license as one of many signs of product maturity. If there is a well established license in place, then that tells me the product is likely pretty stable and this along with other factors helps me determine if I should make the time investment to try and use that product. I think the issue here isn't whether your current users are having any problems with your license, but rather there are likely potential users who haven't even touched it because of the license. Having an explicit license is very helpful in the long run.