My initial impressions are very positive, but further testing is to come tomorrow (+400 km as copilot, hehe).
Finally, the read text is Spanish. The problem with extended characters remains (ñ, á, é...), they are incorrectly substituted by others and the result is comical. And the pause between "at the roundabout take the" and the "n-th exit" is a little bit too long. However, if the instruction is "continue straight /left / right", the pause is normal.
By the way, in the instruction list, roundabout appears translated as "redondel", instead of "rotonda". Is Spanish for Spain or Spanish for Latin America missing?
And regarding the gas prices, in Spain it is mandatory for the stations to send them to the Ministry of Industry. And they offer the whole list as public data (no mention about licensing or commercial uses, though). There are different formats, some of them may be incomplete. The link to that info is (English):http://geoportal.mityc.es/hidrocarburos/eess/?l=sl
EDIT: And this one for the WMS capabilitieshttp://geoportal.mityc.es/cgi-bin/mapserv-hidrocarburos?REQUEST=GetCapabilities&SERVICE=WMS
More feedback after tomorrow's drive.