I prefer it as a nickname, though for Guinivere I would likely use Guin (or Gwin).
In any case, It is a pretty and strong name. It is simple, which is always a plus... and it has some decent history. Howver, I have a slight bias against
Gwen because I have known two and was not fond of either.
However, I have know a couple of Gwendolyns too (one always goes by the full
Gwendolyn) and they were all stellar people. One is quite successful, singing in the
Berlin Opera in Germany.
Just a few middle suggestions:
Gwendolyn PaigeGwen ArletteGwendolyn EliseGwen AmandineGuinivere
JaneGuinivere
SarahGwen EricaGwendolyn HannahGwendolyn JoyceGweneth IreneGwenith GailGwenda FaeGwenda Lonette
Gwenllian Bell
Personally... I like this combo with
Gwen as a middle:
Brigida Gwen Lily