We did the Med on the Millie this past August...The ports are similar to the ones you'll do ion Brilliance and RCI and Celebrity use the same Shore Excursion operators...
We did cruise line shore excursions in EVERY port...and I give my comments in detail on my cruise review which you can find here:
http://www.cruise-addicts.com/reviews/readreview.php?id=0000002441
Just scroll down to the "ports" section of the review where I run down every excursion we did...
On the whole, the excursions were expensive...we paid around $1800 total for two of us for 10 excursions in 9 ports...
BUT, here's my take: How often will you get to these cities again?
And there is SO MUCH to see in each port...
For example, you have a full day in Rome (which is not nearly enough), but why take a $52 half day bus tour? And why spend time in the industrial port of Civitavecchia?
We took the full day $128 "Walk in Renaissance Rome"--which may be the bargain of the Rome full day choices--You get the Trevi, the Pantheon, the Piazza Navonna, the Vatican and a very nice lunch included...And you've gotten to walk Rome, to experience Rome, to really see at least a few of the sights--not just from a seat on a bus...
You can save a few dollars in some ports going out on your own...Dubrovnik really doesn't require a tour...neither does Corfu if you are only wandering the town--but, I do recommend the small price for the half day tour to the Achellion Palace...Villefranch, you can catch a train to Monte Carlo and wander on your own...
But, I would do a tour in Livorno, Rome and Naples for sure...
Venice you can do on your own--buy a copy of the AAA Spiral guide to Venice (about $13.50 at the Auto Club, as low as $10 over the internet) and follow the itineraries...Take a tour of the Doge's Palace and of the Ghetto Synagogues--you can buy the tickets for a few Euros right at the sights themselves...
Again, go visit my review...I hope it would be helpful...and feel free to E-Mail me with any questions...
Have fun...