My guess, based on crude extrapolations from reported nutrients of other dried foods, is that you'll get half the nutrients of fresh mussels.
That ought to be a clear improvement on a vegan diet.
I suspect your main remaining reason for concern might be creatine.
My guesses about why vitamin pills tend to be ineffective (none of which apply to dried mussels):
* pills lack some important nutrients - ones which have not yet been recognized as important
* pills provide unnatural ratios of nutrients
* pills often provide some vitamins in a synthetic form, which not everyone converts to the biologically active form