Application Can Only Be Installed On A User By User Basis?

I have a few programs published via ClickOnce. These are highly specialized programs, and are only used by a relative handful of people, but the set of users is likely to change, and is spread over a fairly wide geographical area. The major advantage of ClickOnce....ok, for me, the ONLY advantage of ClickOnce, is that I can create updates and have them (mostly) installed when the end user runs the program. Over the brief time that I have used it, I have encountered these aggravations regarding ClickOnce:

1) The application can only be installed on a user by user basis (it can't be installed for all users at once). I understand why this is done for a general solution like ClickOnce, but it is certainly an aggravation.

2) Updates don't always appear to happen. Usually, the updates do happen when a person starts the program, but a fair number of times, the update isn't noticed, or recognized, or something. This causes the user to continue with the old version, which makes them think that I didn't fix the bug they had, which causes them to give me a raft of excrement, which results in me flipping them the bird. Much hilarity ensues (fortunately, I'm friendly with my entire user group, so this is a fairly accurate acconting of the sequence of events, except that I just laugh at them rather than replying in sign language).

3) Certificates expire in a year. Certificates are a great thing...for some situations. In my case, an alternative seems like it might be better.

4) Some settings in the manifest are so doggone hard to fix that I've nearly given up. I changed the URL that ClickOnce was supposed to go to for updates, and found it impossible to change the program to find the new location. It had to be there somewhere, and I found several candidates, but never could find the critical one.

Because of these issues, I have been tempted to write my own replacement. There are a few issues that I'd like some commentary on. For one thing, security is an issue that is hard to pin down. None of the data I am dealing with is worth a second thought. No cracking of that data would harm anybody or any thing. However, my first thought would be to have people install an app that would go to a web service to check for the existence of an updated version. If one was available, then the existing program files would be overwritten by the new files. If one was not available, then no overwrites would take place. Lastly, if the service couldn't connect, then no overwrites would take place (of course). If the files were compressed for transport, it would be kind of difficult to intercept and inject a different program into the transport stream, so the only weakness that I can see would be if somebody hacked the server that held the new version, and replaced it with something else. What am I missing here?Also, has anybody done anything like this, and if so, what else am I overlooking?