Depends if it suits your needs. If you are playing just bass and leads, the Microkorg is still good enough.
But if you want to play chords, brass stabs, you might want to upgrade to the XL.
To me, the R3 which the MicroKorg XL is related to, sounds better than the older generation MS2000 on which the Microkorg is based on.
However, it's your ears and you should go down to City Music and have a go at the Microkorg XL before you decide.