Should I get Rick's Prague guidebook (or Prague Pocket guide) in addition to this Central Europe book?
If you're spending only a few days in Prague, Rick Steves Central Europe is all you're likely to need.
If, however, you're spending four days or more in Prague, or at least a week in the Czech Republic as a whole, the extra information in Rick Steves Prague can be worthwhile. It offers more in-depth sightseeing information on Prague, several additional self-guided city walks and museum/sight tours, and more specifics on shopping and entertainment. It also includes all of Rick's favorite Czech destinations outside the capital. (Whereas the smaller Pocket Prague guide offers essentially the same info that's already in the Central Europe guidebook.)
Should I get Rick's Budapest guidebook in addition to this Central Europe book?
If you're spending only a few days in Budapest, Rick Steves Central Europe is all you're likely to need.
If, however, you're spending four days or more in Budapest, or at least a week in Hungary as a whole, the extra information in Rick Steves Budapest can be worthwhile. It offers more in-depth sightseeing information on Budapest, several additional self-guided city walks and museum/sight tours, and more specifics on shopping and entertainment, plus activities for kids. It also includes all of Rick's favorite Hungarian destinations outside the capital, plus nearby Bratislava.
Should I get Rick's Croatia & Slovenia guidebook in addition to this Central Europe book?
Rick Steves Central Europe includes full coverage of the main destinations in Slovenia: Ljubljana, Lake Bled, and the Julian Alps. (Additional Slovenian destinations are covered in Rick Steves Croatia & Slovenia.) However, Rick Steves Central Europe includes only short overviews of the highlights in Croatia, as well as Bosnia-Herzegovina and Montenegro — all of which are covered in depth in Rick Steves Croatia & Slovenia. So, if your itinerary includes only the main stops in Slovenia, this book is all you need. But if you're doing more in-depth travel in Slovenia, or spending substantial time in Croatia, you'll want to add Rick Steves Croatia & Slovenia to your suitcase.
Should I get the either of Rick's Vienna books in addition to this Central Europe guidebook?
If you're only spending a day or two in Vienna, the Vienna info in the Central Europe guidebook is all you're likely to need. If, however, you're spending at least three days in Vienna, the extra information in Rick Steves Vienna, Salzburg & Tirol can be worthwhile. It offers more extensive sightseeing advice, and more specifics on shopping, concerts, and nightlife, as well as complete chapters for plenty more Austrian destinations. (Whereas the smaller Pocket Vienna guide offers essentially the same info that's already in the Central Europe guidebook.)
Should I get the Snapshot guide for Kraków/Warsaw/Gdańsk in addition to this Central Europe guidebook?
No, because Rick Steves Snapshot: Kraków, Warsaw & Gdańsk is simply the excerpted Poland chapters taken directly from the complete Rick Steves Central Europe guidebook.