I'll try to answer all the questions.
We only booked the one excursion because I find the port days exhausting, especially with kids, so I didn't want to overextend us. Also, for the West Coast Cruise, your port days are all in a row! I wanted a pool/beach combo, so I opted for Paradise Beach and El Cid.
We had gone to El Cid (hotel with a huge pool and beach access) several times before (years earlier) and wanted to return and show the kids. I had read (on cruisecritic) that you don't need a dayroom or reservations to use the pool at El Cid. So, we took our own cab and went directly there (I think it was about $15 dollars plus tip). When you walk in, the time share people try to corner you with promises of free food and drink. I don't like sitting in time share presentations (especially with 2 kids), so I told them that I was told I could use the pool without seeing the presentation or paying if we purchased food and drinks. They let us pass with no problems and we used their pool and went to the beach. We had drinks and chips with guacamole and salsa and it cost us less than $20 (but we didn't have a lot of drinks since we only stayed a couple hours). On the way back, we stopped at Senor Frogs for lunch which was quite fun. On this day, we took one stroller, but didn't really need it, since we primarily took taxis. I had trouble finding cabs with seat belts -- I found the shoulder belts in one cab, but neither me or the driver could find the stalks. All the cabs we were in had fabric covering the backseat (clean), but the seat belts were missing even in newer taxis. We brought our carseat, but didn't use it. It made for a very crazy and scary ride which I hated. We picked up towels on deck 9 before leaving and just brought them back with us.
For the excursion in Puerto Vallarta, there were really nice buses that took you to the hotel. Again, no belts, but nice busses. We didn't bring a stroller and didn't need it. We only walked to the lounge chairs and plopped our stuff on the lounge, then we went swimming. Towels were provided when you met your excursion group (before getting off the ship). We opted for the 12:40 excursion, but we left early (the buses pick you up at 5:20 for a 20 minute bus ride). We didn't want to miss Pirate night dinner (great food at the restaurant), so we took our own cab back to the ship.
At Cabo, we just walked around, so we brought two strollers (our 5 year old hates lots of walking). I was really happy that we had two separate strollers because most of the walkways were quite narrow and our really small (Maclaren umbrella) strollers barely fit in a few places. Plus, the walkways are mainly cobble or brick which is tough with small strollers. But, there was no way to fit a good walking stroller with air tires through the small sidewalks. We did the obligatory Cabo Wabo stop which was fun, but really expensive (also $60 for us). All food is served on the second story, so strollers need to be carried up here. Also, in Cabo you are tendered in (small boats dock on deck 1 and you take stairs to the small boats, then the small boats take you to shore). This was definitely easier to maneuver with small strollers (since we had diaper bag, strollers, and 2 kids).
We've traveled in Mexico before and are very cautious about where we eat and drink. Since we've been to Mazatlan, we felt quite comfortable eating and drinking at both the El Cid and Senor Frogs. We also ate and drank at the
DCL sanctioned hotel for the Paradise Beach Resort (I figured that they would make sure water was purified if they were bringing hundreds of DCL cruisers to the hotel) and we ate and drank at Cabo Wabo (major tourist destination). We didn't get sick at all from any of these places. Just thought I'd share since I'm a little wary about trying new places in Mexico.
