If you have a seat reservation in Premium (about €25, as far as I know only bookable at Renfe ticket desks), you should get access to the lounges. If you have a reservation in Comfort (first class seat but no service, about €10-13), you generally do not have lounge access.

However, the Renfe lounges (Sala Club) isn't really worth spending much time in, and in any case they don't serve breakfast there. I wouldn't even head earlier to the station for going in.

If you have a seat reservation in Premium, depending of the moment you will get a breakfast served on board. This was my breakfast on a Saturday last september.

@Schelte Thanks so much for answering my question again :)

I reckon we won’t book premium then, comfort should be enough :)

I do have another question about night jet from Venice to Munich, maybe I should write a separate post.

Booking premium probably makes most sense around lunch or dinner time; for passholders, for €10-13 extra you get a meal and all drinks (including alcoholic drinks) served at your seat during the trip.

I would usually pay less for a breakfast in a café in Spain, so don't think it worth for that. Note in between Renfe's meal times they serve a snack which is worth even less - at least in my opinion. 

When booking at ticket offices you might not be given the option to chose between Premium and Comfort, but ask as they should be able to book both with the pass rate (at least for 1st class passholders). All AVE's offer Premium, and if I'm not mistaken Euromeds as well. 

If you book Premium, be also sure to give up dietary preferences when booking as there is no choice in the meal you get once on board.