We were on the Mexican Riviera in May as part of the Ocean Princess' San Juan - Vancouver repositioning. I can't advise you on any Princess tours as we did not do any on this portion of the cruise.
We 'hated' (not really) Acapulco where our ship overnited. Visually, it's a beautiful harbour at night but during the day it's a big, dirty, hot, smelly, noisy place where you are constantly harassed by begars, 'tourist' guides, and taxi drivers (Cartagena was better). The best thing was the fort directly across the street from the ship. It's an air conditioned museum inside - worth the $4 admission. We walked over to see the cliff divers, and also to Papagayo park where you can get a free drink at the jewlery factory/store. Here we ran into a Princess tour, and thought it was funny those people had paid for the privilege of being 'lead like sheep to the slaughter' - the sales people here were unbelievable.
Zihuatanejo is a delightful little fishing/resort town that is just the opposite to Acapulco - no harassment. We walked to Playa De Ropa. Don't try this - its too far, and way up and over a headland but we didn't know this (the port 'maps' Princess provides are absolutely useless unless you want to shop in one of 'their' stores). It's a beautiful beach, was almost deserted, and some huge waves made for great body surfing; plus, I found a good sheltered spot to snorkel. If that's what you want, just take a very inexpensive cab! (it cost us $3 with tip to get back). This is a tender port and we (supposedly) had only half a day there. At noon there were at least 300 people lined up on the dock in the blazing sun waiting for tenders. We sat on a beautiful shady porch with cold drinks for an hour and a half until we caught one of the last tenders back to the ship. We didn't go over to Ixtapa - it's a 'creation' of the government and is all modern hotel/resorts.
Puerto Vallarta was the best because we 'lucked' into an excursion by accident - after taking a taxi downtown to explore on our own, we were walking along the beach because I wanted to go parasailing when a vendor talked us into a day trip. A power catamaran boat (Luna De Miel) owned by one of the big resorts had left from right beside the ship at 10:00 AM (we didn't know this) and was sailing across the bay over to the jetty to pick up more passengers. For an all-inclusive $25/person, an eight hour trip gave us breakfast & lunch, plus an open bar: all the beer (Corona or Dos Equis), tequilla, vodka, rum, whiskey, soda (anything you wanted) all day! We stopped and anchored at Los Archos to swim/snorkel off the boat (equipment provided if you wanted). The islands/rocks were hollowed out (some completely) and you could swim into the caves or right through the islands' 'tunnels' - clear water and lots of fish (better than Trunk Bay on St. John). Next stop was a great beach where you could stay on the boat or go ashore on small tenders. Parasailing was available here for $25, but we hadn't brought enough cash. We then continued around the Bay to the final stop at another beach where we again tendered ashore. We went horseback riding
(about 20 minutes each way) up to a river waterfall and pool to swim. After
the ride, we had lunch (3:00-4:00, choice of five things) at a cantina on the beach. The 2-hour sail back to the dock (right beside the ship) was a party! They said we would get back at aprox. 6:00 and we were a little nervous all day as we had to be onboard by 6:30. It was 6:18 when there was space at the dock for the boat to get in to let us off....close!....we had JUST enough time to get a postcard for our collection before going back aboard.
Mazatlan was Ok for a large industrial city/port. We went to the Golden Zone - beaches, hotels, resorts, shopping - by taxi (it's about 7 miles away) in the morning, came back to the ship then walked to Old Town for the afternoon. We liked the cathederal/market area of Old Town.
In Cabo San Lucas I cancelled our 'Sail and Snorkel' excursion. This was a good move because people who did go were mad that it did not take them anywhere one could not see from the ship... plus, the water was very cold! We walked around town and discovered the Cultural Center (Casa De Culturo?) by accident. It's on a hill in a very nice park-like setting. A stroll around the marina is beautiful.