Hi Jose
I find one such guide (Lonely Planet, Rough guide etc.) for a Country like Italy or France to be moderately useful. Not for the restaurants, etc. as I think they are overly focused on the city centres and often a decade or two behind the times. However for a simple way to look through places that might be worth exploring in more detail, or for a simple set of logistics (e.g. regular buses and trains from the listed locations), then it's got use.
I don't update my old copies though, as I'll always be writing my 'crib notes' from more up to date specialist sources (often online now).
Italy has been our main focus and for that I've found some specialist resources that have been massively more useful
1. Fred Plotkin's Italy for the gourmet traveller. Oddly not so much for the restaurant and shop suggestions, which aren't comprehensive and too rarely updated. However as a writer giving you a feel for the different places, I find him exceptionally good. He is a very engaging writer and can entice with his descriptions of the regions, towns, etc. It is his guide I'll often reach for when shaping up the 2-3 destinations of the trip.
2. Golosario. An annual listing of fine food shops & producers and it is very thorough. Occasionally they'll miss a really good place, but more often than not they'll have them listed. It is a real celebration of the fine food traditions (and modern innovations) in Italy.
3. Duemilavini. Sadly now online only, and I miss reading their wine tasting notes. However in the back was a listing of restaurants and bars/enoteche where wine is taken seriously (the book is published by the sommeliers association, so they are champions of places that care about wine)
On top of that, I'll often use googlemaps to scout out the local area, from cafes to ice-cream shops, to where the local post offices are. This occasionally highlights a new place of interest, or sometimes something less fancy, but convenient enough to want to know about e.g. a pizzeria
My criblist is obscenely long for the amount of time we're spending in a location e.g. 15 restaurants for a 3 night stay and might include 10-15 places for a village we might or might not visit. It is never a 'must do' list, but always a convenient list of options that I am confident will be interesting, good or both. We still trust our own instincts, either trying something not on the list that looks good, or deciding against a place on the list which doesn't look as good as anticipated.
For a modern way to do this, creating your own labelled map in Googlemaps can be very easy to use on a phone. I did one for Torino and have added to it with later visits, as new places are identified, or others close. The idea is that if you're getting towards midday and feeling hungry, it's lovely to be able to bring up 2-3 good options in walking distance.
I hope this helps
Regards
Ian