Dried herbs really do only last around six months, certainly no longer than a year. They're generally easy to get in small quantities, though.
Spices are trickier. They'll generally last rather longer, but the time will vary. If the spice is used for the colour and/or heat (e.g. turmeric, chilli) it will generally last much, much longer than one used for its smell and/or taste. Whole spices last much, much longer than pre-ground; I generally buy whole spices from asian stores, they sell them in much larger amounts for the same prices as supermarkets; and use a coffee mill to grind the right amount just before cooking (and keep a separate one for coffee!).
If kept in the dark, in a dry, clean, airtight glass container, spices and dried herbs will certainly not become health hazards, and should not pick up unpleasant tastes or odours. The strong-tasting / strong-smelling ones will, however, lose taste and smell, eventually almost completely; since that is the whole point of using them, you might as well not bother once they're off.
Best Answer
Fresh spinach, like other leafy greens, is best stored in the fridge in some way that keeps it dry but not too dry. The things that cause spinach to wilt and spoil are:
I've included a number of references below, but here's my method that allows me to store fresh spinach for up to two weeks:
This way, fresh spinach can keep for up to two weeks in the fridge. If you need longer than that, then chop, blanche, drain, and freeze it.
Resources: