I can make the drive from Rome to the port in about 1:15...but tour buses seem to take a bit longer. On Sundays, they might be able to save 5 - 10 min. The issue of these darn buses comes down to the ridiculous cost. Most of the cruise lines charge about $70 per person. For a family of 8 this would be $560 just for transportation. The train costs about $20 round trip (not sure of the current exact cost) which also includes use of the subway in Rome (you need to request that type of ticket). The train is also faster. The port buses (ship to port entrance) are very nice and free because they are provided by the port authority. As to you being worried or "nervous" about going on your own, that is exactly why the cruise lines can charge very high prices for tours, and folks line-up to pay those big bucks. When we travel on cruises, we are often approached by fellow passengers looking for information and "encouragement" to go on their own in ports. My reaction is that if they are going to be "nervous" simply pay the big bucks and take the tours. Or course I do not usually disclose that I am a stockholder in the two major cruise lines and love to see others feed the profits
Yes, the "tours" are a nice profit center as are the Art Auctions, Bingo, slot machines, and of course the new fad of the decade called bottled water.