Depends, if you're hitting any limits or bottlenecks.
Performance would normally be one of the main reasons to upgrade or unable to expand due to limits of the platform.
New systems offer loads of benefits over the fas3050 range ... mostly all of the would however be expandability (e.g. 10G nics, pam modules, more shelves, larger drives, 4gb loops etc.)
Software wise you shouldn't worry that much, you can still run latest and greatest version of ontap on a 3050, you might however miss out on some features which are only available on 64-bit platforms (e.g. fas3x40/3x70).
-Robert