slant valve springs

I purchased some engine builder valves from E-bay item no 380919173128

I am also considering these 340 valve springs E-bay item no 390854240085 but I am thinking for a non high revving engine I may be wasting my money, that the stock valve springs will do just fine.

From what I have read a stiffer spring will put extra wear on valvetrain components and I am going for longevity with the engine. Not a racer.

What is your opinions on this?

Also can someone share with me how they test their existing valvesprings at home or is this something a machine shop can only do.

Recently D.I ( over on slant.org ) wrote within one of his posts about finding a couple of weak valvesprings on an engine/head he was working on and so Id like to also find the same potential problem if it is there.

Is it recomended to just change out to all new stock valvesprings when re-building an engine and if so are these springs still avail for a good price?