We've stayed at the Porto Rocca in Monterosso in late August/early September one year and enjoyed it. The Porta Rocca sits high above the sea on the south end of town, and is therefore in a quieter location -- the terrace makes it feel like a private villa. This location is also away from the more major development in Monterosso, but it is still an easy walk to everything. An issue for some: the last few yards to the hotel from the public walkway is up a rather steep driveway (my senior-citizen mother would have problems, but if you plan to walk the trail, you should have no problem.) Half board was required, but the menu was varied enough and delicious, excellent multi-lingual service staff. Charming bartender in the cocktail lounge. The PR also has its own private beach-chairs area, which is useful as the beaches in the area are the typical pebble-stone variety. If you book, let them know your arrival time and they will collect you at the train station.

YEs, CT is touristly, but it's not oppressive, and serves its purpose. There was a town dance on the stone boat landing, and occasionally musicians playing open-air that could inspire a tango or rhumba among the onlookers. I like the older section of town (south of the pedestrian tunnel) for being a little less congested, but it's intersting all around.

A caution: the trail can be a little trying from Monterosso to Vernazza and Corniglia, i.e. high, narrow, no guard rails, etc. The trail is easier that connects the southern towns.

Monterosso itself has easy train connections to many of the destinations you'd like to visit.