Joe,
Your NOT being overly cautious, but I do think your not thinking outside the box. The box being your 1 Meta Description you are trying to use.
Think about it this way, you cant control your customer, and you cant control their mind, you cant control what they search for. So your perceived problem is actually an opportunity to have 20 ways to describe your 1 Meta description. If the meta description your going after is "Pet Products" the chance that 100% of you audience is going to be searching for that exact term is pretty slim. One customer may search for "Pet Shampoo" yet you want them a customer or at least the opportunity to sell them "Pet Products" as long as they are a vertical, you might sell them something else.
So in my opinion you actually have 20 opportunities to optimize those pages for different keywords and cast a wider net at capturing a customer for your website.