I have the Donegan also, but I didn't know that until I just now went and looked at it. I guess it's 4x- it has a raised "4" on the lens piece. I've owned it since way before this line of hobby, when I was a serious model railroader in N scale (1/160!!!).
Over the years I've replaced the tightening knobs at the temples because they come off and get lost to the carpet monster, but that's about it.
I'm a four-eyes anyways, with bifocals, but don't need the lower part of my own glasses with the visor, which is great (more in a minute).
I saw this thread and it struck me; I cannot think of a tool I own that has by itself so increased my abilities, except maybe my airbrush, but that's just technology, and expensive too. What I mean is that I could not do the same task without as I can with, by a really BIG difference. I always wear it now when I model, flip up/ flip down.
One time I had a particularily obnoxious client who kept arguing contract terms well into the phase where I was working and billing. So I called him and went over to his office to go over the contract; pulled out the old O/V, put it on and sat down at the conference table. It certainly broke the ice and cost a lot less than bringing my lawyer along.