My personal opinion is no. I think there are better emulations of a 303 in software these days. If it was me I'd look into buying software. I've got really into Ableton recently, and this coupled with some VSTs has made me far more productive. That being said I know others that work faster with grooveboxes - it depends on how you are wired.

The best boxes I've come accross are the Machine Drum, and the MPCs. I didn't think much of the Roland stuff, and I've never played with an Electribe.

Hope this helps in some way.