Yes, you absolutely should put a data system in front of a radio on the priority list. No other single item, IMO, will provide as much bang for the buck to make you faster, and in such a way that will transfer easily to any car you drive (both the technique learned, and the system itself).

GPS-based systems seem to be the better way to go these days, due to easier installation.

You should consider reviewing my data acq. presentation - it's linked off the main Waterford Hills page (www.waterfordhills.com) - to see some more detail and options (though you've already had a good exposure, sounds like).

Radios are nice, I have them too, but they really don't make you faster.