Steve,
A HouseBot Task should be faster than a VB Script. Although VB Scripting is pretty fast, it still has to load the VB engine, load the script, and finally, interpret and execute the script.
Anything is possible, but it's doubtful that the task is missing a change. When you save a Task, it will register itself with each Property that is part of it's condition. When a Property changes, it will run thought the list of registered Tasks and evaluate them. So if it works right for one PV change, it should be working the same for all.
As a side note, the next version will have a Task condition option for each Property to allow you to exclude it from task evaluation. This can be helpful for things like when you have a time property in a condition, but don't want the task evaluated every second (this probably won't make sense unless you have been through it

)