My guess is that a separate quick entry application would probably use the same amount of resources, so what's the point? I think Omni Group's technical judgment should be trusted here.
Now, it just occurred to me, that what Omni may be able to do, would be to have a small deamon that launches at startup and listens for the OF quickentry keyboard shortcut (or clipping or whatever). When this happens, OF could launch as a hidden app (no dock icon). When a user then sends OF a Launch event by double clicking it, it could then appear to launch, but would really just become un-hidden. (I don't mean a simple hide like you can do now, but a run as a background app).
A quit event would still quit, but the listener would stay open to repeat as above.
Not sure what technical hurdles would need to be dealt with, but it would seem to resolve this issue (I personally don't mind it open all the time, but I have 2GB)