I started flying 737-200s in 1981 and remember a lot of departures with contaminated wings. The airplane never seemed to "notice" and it was accepted practice. All we had then was Type 1 and, when we did spray we would often sit around for what now seems like a l-o-o-o-ng time! That's how it was until Dryden came along and smartened us up.
I remember a light going on one day when I read an article on simulated contamination. I think the researchers used sandpaper to simulate contamination. Their results showed that performance was not degraded a great deal as long as both engines were operating. I had my eyes opened by a set of results that showed only a slightly degraded climb rate with both engines operating but a negative value with one engine out!
It seems to me that these airplanes will more or less "muscle" their way around the sky with both fans operating but if you lose one with contaminated wings you are probably going to make a big hole in the ground.
If the airlines want to save money on de-iceing then they should invest hugely in an alternative measure. As for me, if I can't decide I spray.