I've got probably 400 miles of street driving, maybe 50 passes and 12 months of sitting for winters. How would I know when it's time to change them out other than a pressure test? what symptoms am I looking for?
I can't tell you what I have for springs off hand but cam is a .725" bullet solid roller.

other than a pressure test which is the standard way to tell, it's usually once the valve float from a soft spring has worn away the keeper groove on your valve stem & the valve has fallen into the piston!
ask me how i know.

dude, spend the bucks n buy a tester & a valve spring removal tool. we pull ours every off season to test & it's the only way to get accurate readings. i had one of those on engine rocker arm testers but 3 of us did the test on all my valves & we all got different readings. the bench tester is the sh!t when it comes to consistancy. my valve springs dropped 10lbs after the first year, 4 years later on they haven't dropped another lb. thats peace of mind especially when my previous springs failed badly on their second season. the tools were cheaper than the wallet pain of the repair.

One other method of checking and storage - There are tools (moroso?)available that hook onto the rocker arm and use a torque wrench to test with. I use one to check mine, and it reads about 280 inch lbs = 320 lbs pressure. If you have a known spring, you can get a reading from it and compare to the others. For the winter just pull the rockers after fogging the motor.

Yes, I'll have to buy a tester I guess. Is there any obvious signs when they are getting weak other than valve float- does the performance drop notably enough to tell by the seat of the pants?
I fear the thought of taking my rockers shafts off- when your engine builder tells you not to take them off for the winter cause the threads are "iffy" that can't be a good sign....

1. free length changes on only some springs
2. some springs are slightly bowed
3. fret marks on the spring seat