That's an interesting outlook on it and to me makes sense. I don't know if we (Airwarriors) have had an "declare emergency" discussion yet, or at least recently but I'm curious what other communities think.
I don't like to think there is a defined threshold for when to declare an emergency. There are some many factors such as weather, fuel, sea state, my position in addition to the state of the aircraft.
As a RAG IP I always used the Land As Soon as Possible as the starting point, assuming the aircraft is handling OK.
If the aircraft is not handling normally but it's land as soon as practicable, do I want crash next to me in the event I goon it up? If so, declare.
Am I capable of getting an expeditious landing? If I'm coming back and I feel like I'll be OK for a few more minutes (before the seat cushion goes fully up my exhaust port) and I'm told I'm #4 behind 3 aircraft in the GCA pattern, then I'm declaring.
Now that I'm on the other side of the "red phone" I can saw we'd rather have you declare an emergency for stuff you are unsure if it rates an emergency than not declare and have issues on short final. The Fire Rescue guys are sitting around anyways (and they're paid whether they roll or don't) so they would rather you be overly cautious and declare.
From the tower side of things, it may make things a little more challenging because we have to start sequencing aircraft to give priority to the aircraft with the problem, but that takes less than two minutes. And it's actually good for our junior controllers to see the senior guys handle the minor emergencies more often.
They can see the process for notification, moving aircraft and controlling the airfield when someone declares and emergency.
Much like the aircraft, if a junior pilot can see a senior pilot handle EP's calmly and professionally, it will demonstrate how that junior pilot should perform when he/she is the senior pilot.
I always imagined an airport going to complete GQ when an aircraft declares an emergency, but that is not the case. Tower does it's thing, Radar puts folks into a Delta pattern, the Fire Rescue guys have to stop watching TV/Working Out/Cooking and man the trucks and of course the Base Ops O gets woken up from his afternoon "snappy nappy".