Advice for Paris to Cinque Terra

I'd probably fly, but since you are investigating all options there is a night train:
http://www.seat61.com/thello-train-from-paris-to-italy.htm

It has a couple of advantages, and would certainly deliver you to the CT earlier than any other option.

The train station is Santa Maria Novella and you can get from the airport via taxi or bus. You will have change trains at least once in La Spezia, but you may have 2 changes depending on the train. You can see train schedules at bahn.de/en or trenitalia, but for me trenitalia does not work as well. Have you posted your questions on the Italy forum?

According to the timetables on both trenitalia.com and bahn.de, you can leave Milano Centrale at 11:10, connect at Genova and Sestri Levante, and arrive in Vernazza at 14:24. Connection times are short, but easily doable if the trains are on time. You will NOT need to go via La Spezia.

If you're flying, the closest airports to the Cinque Terre are Pisa and Genoa. Use Skyscanner to find flights: http://www.skyscanner.com/

From Genoa Airport, you would take a bus or taxi to one of the Genoa train stations (there are two - Principe and Brignole). From Pisa Airport, there is a train station right in the airport, but I think Roberto posted that train from there to the center is out of service right now, so you may have to take a bus or taxi to Pisa's main train station.

From either Pisa's or Genoa's train stations to Vernazza, use either the Trenitalia website http://www.trenitalia.com/cms/v/index.jsp?vgnextoid=4ddd1a035296f310VgnVCM1000005817f90aRCRD or the Bahn website http://reiseauskunft.bahn.de/bin/query.exe/en to find routes. Use a date within the next 7 days to show all the options, since some of your trip will be on local trains, and these are only loaded for the next 7 days.

emily,

One other budget flight option to consider is from Paris / ORY to Milan / LIN via EasyJet, which has a departure at 11:00, arriving 12:25 (current price listed at €67.98, but this will increase as the flight fills up). LIN is relatively close to the city, so it will be easier to get to Milano Centrale than from MXP. The train from Milano Centrale to Vernazze will be about 3H:20M, often with one change in Monterosso. While it may be slightly easier to fly inbound to Pisa or Genoa (in terms of train connections to the Cinque Terre), this is still a reasonably short trip.

The Vueling flight to Florence that you mentioned would also be a good choice, and will probably get you to Vernazza at the earliest time. There are no direct trains on that route so you'll have to contend with one or two changes. When you arrive at FLR, I'd suggest taking a Taxi to Firenze SMN station as that will be the quickest method. They have a flat rate for fares, and as I recall it's about €28 (but my memory is a bit foggy on that).

IF you're able to get to the station quickly, you may be able to connect with an 11:53 departure (more likely if you have carry-on only), which will arrive in Vernazza at 15:30 (one change in La Spezia). The next departure appears to be 12:28, and that has two changes in Pisa and Monterosso. One portion of that departure will be via InterCity train, which has compulsory reservations. Many of the trains on that route are Regionale, so DON'T forget to validate your tickets prior to boarding the train on the day of travel, or you'll face hefty fines which will be collected on the spot!

"it looks like the earliest train from milan central to monterosso isn't until 12:10pm"

That's not the case. Which website are you using to research train times? I counted at least nine departures on that route, beginning at 06:10.