Springs: How do you know?

[Alec]

Since this forum has been on the topic of springs lately I have some Q's...

How do you know when your springs are bad?
Its pretty easy to know when the shocks are shot but what about the springs?

I have a wagon (85, 295k) and I was thinking about new springs (primarily rear).

I am also aware of heavier springs that were available for different versions of the wagon and sedan. I tend to carry a lot of 'stuff' in my wagon and could probably use the extra support. Any thoughts on heavier springs? May interfere with ride height?

Thanks for your time,
Alec.