Unfortunately cost does have a significant impact otherwise we'd all have smoke hoods and every plane would be fitted with defribs, life rafts and survival kits.
Your example assumes accidental inflation of the life vest. If the incident you refer to is the one I have in mind then the problem was passengers deliberately and concisely inflated the vests prior to touchdown sealing their own fate.
I should imagine the amount being accidentally inflated would be minuscule and even then there is a way to deflate by using the tube. With your suggestions making it more difficult to operate the vest it is not hard to envisage that more people will die due to not being able to inflate the vest as opposed to those whose life jacket inflated by accident and not their own doing.
The current jackets are just fine if you follow instructions and use the correctly. All I can see with your suggestion is lots of people bobbing in the water frantically trying to inflate the jacket before they succumb.