The "Full" Nero vision comes with the non oem version.
It is rather far more capable than the "express"
I am not sure if for
editing it does more than WMM which is actually a good ( if fairly basic) starters editing program . I have really only used it ( nero vision) to knock together a DVD in a hurry but just glancing at its feature set it looks comprehensive.
As an aside, you should not really lose Picture quality with WMM if you capture as DVavi and output as such.
Some people like WMM You can find them
here
However If you get hold of Nero 7 , It has the "full " Nero Vision 4.
You will be then be able to compare the editing abilities of the full Nero Vision4 vs WMM2 ( you do have winxpsp2 dont you?). It can certainly output to DVD which WMM can not.
As to your last question. It is ok as YMMV.
As time goes on you may wish for more ( and have to spend more

)
HTH