There's no questions that instrument flight is a good skill to have, maintaining currency, even in IFR operations can be a bit tough unless you get lots of actual cloud time, VFR on top may count in a log book, but it does not make you work. To that end there are several PC based flight simulators that allow you to "blank out" the visual clues by setting a cloud base and now you are left to navigate by instruments alone. No substitute for actual IFR or training for such, but certainly a worthy pursuit if properly considered in an overall currency program.