During our 4-night cruise this past April, we got to experience both a stateroom with a verandah and an outside stateroom with a porthole. We had to spend the first night in the latter because they had to fix something in our original stateroom (the one with a verandah). The stateroom with the porthole was very nice and spacious, and the view out the porthole was gorgious (it was one huge porthole!). However, nothing beats having a verandah!
Whenever the public decks got crowded, we'd head back to our stateroom and enjoy the Caribbean sun on our own private verandah. That was soooooo calm and made all the difference to us on that cruise. We don't have kids yet - I guess with kids we would spend more time by the pools. We're not big on all those activities offered during the day. On a Disney cruise, it's all about relaxation for us as we combine it with a WDW stay (which is the more active part of our vacation). So it makes sense for us to spend the extra money and get a verandah.
Another very important reason for us to get a stateroom with verandah is that I get seasick if there's rough weather. And of course we hit a cold front with LOTS of wind during our cruise
(Even the crew said they're not used to such rough sea conditions). So when the ship started rocking too much (mostly in the evening), I'd step out onto our verandah, look out onto the ocean, smell a fresh sea breeze, and feel much much better instantly.
I think what stateroom to book depends on your personal preferences. A lot of people (as stated above) prefer to spend the money they save by booking an inside stateroom on spa treatments or excursion. Others state that they don't spend much time in the stateroom anyways. For DH and I, it's worth spending some extra money on a stateroom with verandah simply because we spend a lot of time there. We both feel that it gives us better value for our vacation money than spa treatments or expensive excursions would. Like I said, it all depends on your preferences.
Lastly, let me say that if we don't have the extra cash to spring for a verandah for a future cruise, we'd definitely rather book a porthole room than not go on the cruise at all. Inside staterooms, however, are not for us as I really like natural daylight. Then again, if that's not important to you and/or you know you won't spend much time in your room anyways, inside staterooms are an excellent way to save money!
I hope this made sense. Bottom line, my advice is to set your priorities and decide on a stateroom based on that. Since you'll do both the Western AND the Eastern Caribbean cruise next March, why don't you opt for an inside stateroom for the first cruise and then one with a verandah for the second? You'll have something special to look forward to, then.
Good luck! Let us know what you decide on!