I felt my rear tire going flat today ( I could feel the bike trying to stand up in a 50 mph lean on a freeway on ramp) (low tire pressure will make your bike want to stand up in the turns) and I rode straight to a service station, got out my plug kit and plugged the tire. This is my work bike. I travel at over 100 mph regularly on it. A plug is not as good as a new tire but think of it this way: If the plug fails, it is just like you picked up another nail, right? If it don't fail, you ain't gonna know the difference between a plugged tire and a not plugged one.
If you get a new tire and ride at 100 mph (or any speed) you can still get another flat, right?
Plugs don't bother me in the least. A flat is a flat. Some release the air slowly allowing for a plug and sometimes all the air is expelled and you ride it flat until you get to a safe place.
Again, if a plug fails, it is only another flat. You can't see a flat coming, it just happens. If it holds, then no worries! Save yourself some money. Plugs are cheap. My .02