I'm plugging Via Vai again because I really think this place delivers a fantastic meal at a reasonable price- if you know how to navigate the menu.
First thing you should notice upon entering Via Vai is the wood fired oven with a four person team (on weekends) tossing together and toasting up pizzas at a rapid clip.
If you catch a glimpse of that scene and *still* opt for a plate of pasta at Via Vai, you should expect zero sympathy for your possible disappointment.
Now... about the pizza... it is a thin, crispy crust composed of a very light flour with a sauce that is not a sauce, but simply tomato.
This is rather delicate stuff, especially when compared to the typical American pizza that is built to survive a bumpy ride in a hot bag while squealing around the hills of SF in a beat-up mini toyota truck in route to your couch.
Therefore, don't even think you can pile six different toppings on this fragile little pie without compromising the overall balance and texture that make it so special.
Stick with the Margherita.
If you insist, try one topping (the mushrooms are particularly nice) but, I have learned through experience that whatever interesting flavor one achieves with toppings may be countered by a significant loss in texture.
To compliment your pizza, stick with antipasti items (the calamari is surprisingly good) and/or salads (my favorite is the baby spinach with slightly warm pancetta, egg, balsamic vinegar dressing).
I can not, however, recommend coupling your pizza with entrees at Via Vai. They are simply too hit or miss and to make the pizza anything but the star of the show is to miss the purpose of Via Vai altogether.
Another plus about Via Vai is the reasonably priced wine list, with mostly Italian and Californian selections.
On my last visit we ordered Isole e Olena's 1999 Chianti Classico for about $30 and a 2000 Pinot Grigio Collio for about the same. Both were fantastic and well suited to the meal.
I can not recommend Via Vai enough, provided you stick to the strengths and avoid the weaknesses.
And, if you have read through this post and *still* insist on a plate of pasta at one of San Francisco best Italian-style pizza restaurants, then the weakness is not theirs at all, but yours.