I have no direct experience but I can give you what I know from reading I've done and people I've spoken with.

First, the valvetrain like is mostly dependent upon rpm and depending on which version of hemi99 you get, there varying degrees of "good" with the valvetrain. There are two different rocker stands, a two and four bolts with the four bolt being the better of the two. This was to deal with the higher spring pressures. The other thing that I've heard is that this motor is peaky when setup like the pro stocks to run at maximum rpms leaving a very fine tuning window if you were looking for max performance.

In regards to spring life, barring no over revs, a friend of mine that worked with a well known Comp Eliminator engine builders race car told me they went the entire season(40-50runs) without changing a spring in a motor that crossed the line at 10k. What typically happens is that more people err on the side of caution and change springs more often than necessary in motors spinning that type rpm. Once the 10k line is crossed however, spring life decreases significantly.

If you had and unlimited budget, I believe the best way to make an engine like this more friendly would be to order a custom tall deck block like what Rick Corn has done so you can stroke the motor and decrease the rpm range. Of course you would have to massage the combo to get it right but it would be a good strategy to increase spring life. Those are the things I've read about the most that come to mind, I know there are also a few different blocks out as well with and w/o skirts as well as varying numbers of cam bearings.