In the future, I'll probably still play 13a, but not 18a.
The problem with the "you can always skip it" argument re: 13a is that if the group in front plays it, you're screwed. You likely won't have quite enough time to go past them and get clear, so you're stuck sitting around. And if you are just going to sit around, you may as well play it.
At least with 18a if you decide against playing it, you're done, so it doesn't matter.
13a was my favourite one-shotter on the back nine, so I think it's a pity it doesn't really fit.