I'm having difficulty understanding what makes this both "unwise, and a waste." Not enough information was furnished by the OP; there is more about this case that we don't know than what we do know.
OK, yes, we don't know everything. I assumed a few things to make that statement.
If you are taking a conventional panel and picking up all the zones at the panel, not changing out all the devices, typically its a money issue. (isn't it always)
If the tampers were commingled with flows then yes by all means. If there were just tampers on a conventional zone, then put the module at the FACP. IMO.
The unwise comment came out of a specific situation that I had it mind. Since none of us are mind readers allow me to tell you: I had a 180,000 sq ft 6 six story mill building. It was wired by, probably 800 different guys and was a nightmare. The conventional FACP had a terminal trouble (double entendre?) . We received the OK to just pick up the conventional zones at the existing panel location and put them on modules there. There was no plans/requirements to upgrade the system, so this was the most cost effective. The reason I feel sending the SLC out throughout the building was bad, is because of the wirings exact condition was not completely known and it worried me that having 20+ legs of SLC without isolation modules leaves you open to having the entire loop go down from one short on one of those loops.
I know, this is not the situation in the OP, its not always unwise, it just needs to be tempered with good planning, which is often overlooked in retrofitting FACP's