I read that giving strawberries a vinegar bath will keep them fresh for up to 2 weeks, but will they be sweet? I haven't tried this yet, but would like to make chocolate covered strawberries for the holiday and don't want to ruin it.
Ideally strawberries should be picked the day they're eaten. Adjusting your shopping plans to the day before or so would be best in any case. I've never heard of this vinegar bath trick, but I've sometimes kept strawberries overnight that I had mixed with lemon juice. They're not less sweet, but the texture is blah, going on mushy. I would experiment at least a day or two with your vinegar bath before relying on this for an actual holiday.
There are two ways I know of that vinegar is used on strawberries.
First, and this is the method I believe you are talking about, is as a wash. The berries are not left in the vinegar, they are simply rinsed in it, normally a vinegar water solution. It is used to clean them, and the theory at least is that the low Ph of the vinegar will kill the nasty stuff that speeds spoilage. Normally this is a watered down solution and is not intended to change the taste of the berries, only extend their life. This should not majorly change the flavor for applications like chocolate covered, but you definitely would want to be diligent in making sure they were dry. I personally have found this to marginally at best extend the freshness but others claim better luck. Typically I have seen common white vinegar used for this.
The second way is in macerated berries. In these, the berries are normally cut and sugar is added. Some use lemon or regular vinegar, but balsamic is what I generally see recommended. This has some effect of keeping the color and some firmness to the macerated berries and is often promoted for that. It really is not the main point IMO however. It is as a flavor enhancer, especially when going with a better balsamic. For this, it is recommended to not use enough that you really taste the vinegar or lemon. Then it becomes a mater of taste, but to those who use this method to makes the freshness and flavor of the berry pop and become more bold. This is a different treatment than what you are looking for, but with just a quick search for methods the two can become confused.
The vinegar bath could be used in your application, but I personally would not expect it to extend the firm, fresh qualities more than a day or two at best.