RalphDill,
I'd say that there are simple ways to avoid the problems and frustration you have experienced.
Personally I have never lost a playlist. I established my main library over 7 years and six major version changes ago. I have moved my media files numerous times from a PC to another and between various internal, external and networked drives without losing anything.
When a new build of the same MC version is installed it doesn't touch the library (aka database) files at all. On the first run it just uses what you already have. During the development stage JRiver has sometimes changed the storage format of the database files, but these rare changes have always been tested before the public release and so far I have not seen any problem reports. Just installing a newer build does not invoke any mechanism that would broke the file links or invalidate the existing playlists. There must have been some additional factors that have caused it to fail in your case, if that is what happened.
When there is a major version upgrade (for instance, from MC13 to MC14) the installer is programmed to offer to use your existing library and also that works for the majority of the users. If you have a more complex setup with several libraries you must add the additional libraries by hand, but that is expected and should not be a problem for someone who has created the additional libraries and is using them.
I hope your drive letters are not changing daily or so, because that kind of behavior is not expected and should be avoided. An MC library is always based on the imported media files and their filenames (including the paths).
If the files disappear from the previous location the default settings in the Auto-Import feature will cause them to be removed from the library. That will also cause them to be removed anywhere they exist inside MC, including the playlists. It would be better to move the files by using the tools that are available inside MC because then the file links would be maintained.
However, you can temporarily disable the auto-import feature or at least the "Fix Broken Links" auto-import setting and mass change the file links by hand if you have reason to move the media files outside MC. I have recently explained the procedure as a few simple steps here:
http://yabb.jriver.com/interact/index.php?topic=55547.msg377589#msg377589and here:
http://yabb.jriver.com/interact/index.php?topic=55224.msg375699#msg375699In case something goes wrong you can always restore a library backup file and start over. MC creates them automatically from time to time, but I'd recommend always creating a new backup file manually before doing any major changes. (File > Library > Back Up Library...)