What kind of soil? Potting mix, garden soil? If you are buying a soil then there is no concern. Buy on sale and save. If you are using potting mix, there are those that demand that you get fresh potting mix every year for optimum growth in pots. I do no hold this belief. While the potting mix does degrade over time, I've used potting mix from the previous season and never had any problems. Also very old potting mix that no longer is good for pots is still great for garden beds.

Nothing wrong with a few worms or bugs in your soil. I've never opened a bag and found any though. I am certain they crawled in (either at the garden center or your house) and did not come with the soil. If your garden center gives you a discount for an open bag then that is a great deal to you.

Well, when I pick up my bags from say, Home Depot, often there is some sort of tear or hole already in the bags before I can even get them off the shelf. I never remember them giving me a discount though for that. But it's always apparent when I pick up new bags, there is ALWAYS lots of soil spread around all over the skids from the bags previously on top spilling stuff out as well.

I thought it would be ecconomical to buy some large amounts during a sale, even if I won't need them for a year or so, but the odd time I read that you should always try to get soil fresh. Anyhow, most my bags are just garden top-soil so I guess it is no big deal.