Hi, davideves...

The comments re: reducing your volume of shared files, at any one time, is intended to actually increase the number of others sharing those 'rare' files - So that they cease to be 'rare' !

As I mentioned, it's only a matter of noting how many other 'sources' there usually are for a given file. If there are numerous others sharing the same content, than it makes sense to stop sharing the same file yourself and thereby improve the chances that you will have an Upload Slot available to someone who wants the 'rare' goodies.

It is quite amazing to observe the process involved in sharing something quite rare... After a short while you will begin to notice the 'sources' for that 'rare goodie' steadily increase - And, you know that YOU did that ! Nice.
It is all basically about increasing the total volume of material being shared, not increasing the numbers sharing the same material. (In only the past two years, the variety of 'content' available on Gnutella Network has increased enormously...
And, we all hope that growth will continue !)

On the 'hashing problem' - Perhaps there is some misunderstanding here and that the situation is not that your shared files are hashed again on every launch ?
And, can you check to make certain that your files that contain the 'hash data' are not being deleted for some reason or possibly being saved in an incorrect folder ?
And, as Peerless mentioned, check the shared files ratio which should also serve as an indicator of the status of hashing progress... That's the most simple way to confirm whether or not the hashing is re-starting at zero or simply continuing towards completion.

Last... The [Edit] up there... Not allowed to make specific references to copyrighted material.
(But, hey... At least I didn't do it in Red, as is normal !)