correct, wiping the cache's will not loose data.
if you do a nandroid backup then wipe data then you will obviously loose your data. that is what i meant to say and it seems as if what you were trying to get at in your question. at least that was how i read it.
as far as keeping data onto another rom, the answer is no and yes. you can use titanium backup to backup your apps and your data. in tb just make sure not to restore any system data as it will most likely contain data and bits of your previous rom and add it to your current rom creating all sorts of bugs force closures and it will not run right. so never restore system data.
you can back up your contacts by attaching them to google rather than your phone that way when you flash all you have to do is sign in to google and your contacts are there. also most messaging apps can move the data to th sd card. other then that they will get erased.
the key to clockwork mod 3.0.0.5 is to wipe dlavik cache, cache and data at least 3x. and you can't use the vr superwipe unless you downgrade your recovery. your recovery only supports edify scripting while most things that can be flashed are in amend scripting. so somethings you will not be able to flash like the vr superwipe. amon ra 2.3(the one i recommend) and clockwork mod 2.6 supports both scripting. you can get them here along with instructions:
http://androidforums.com/evo-4g-all-things-root/259446-clockwork-amon-ra-pc36img-files.html