We are aware of the problems that vBulletin has with mobile access and viewing banner graphics is one of them. I'm told that there isn't anything we can do about mobile access which is a major reason we want to convert to Xenforo. I think I remember Aaron telling me that about 40% of the access here is with mobile devices, mostly phones.
Another concern is that the search option is terrible and I have always felt that our archives were as important as active threads, particularly the pictures and other file attachments we host.