I now what you mean. to re-render the current frame you'd have to kill the viewer before clearing the buffers.
Here is a proc to reload all Read nodes:
proc reloadAll {} {
foreach cur_node [nodes] {
if {[class $cur_node] == "Read"} {
knob $cur_node.version [expression $cur_node.version+1]
}
}
}
You could wrap up all three things into one proc and call that as "clear Buffers" (I can have a go at that later if you want).
It also doesn't seem to speed up any calculations after a slow down
That's weird. Check the script info when the slow down to see if there is a trace (alt+i)