Almost all depictions and pics of battles I see show them just using those regular kimonos, no helmets or armor. Even old Kurosawa movies depict them as not using those kind of armor. I also remember a book about Musashi saying he resembled a homeless.
That makes me think the armors were mor of a symbolic and ornamental thing, rather than a real war gear.
Were those armors used in battle at all? How widespread was it?
First thing to keep in mind when talking about samurai is how large a period of time you are talking about. The start of the samurai period is debatable, but if you use the Gempei war as a rough start date, you are talking about nearly 700 years, and as you might imagine the answer to your questions vary a great deal over that period of time.
The ornate armour, including the masks (mempo) and helmets (kabuto), were indeed worn during battle up until the end of the Sengoku Jidai. The armours following this period were increasingly "ornamental" (or "gaudy" might be a better term...) but by this stage, they were indeed purely ceremonial. As with armour in Europe, samurai armour was incredibly expensive, and the richer a samurai was, the more extravagant his armour would probably be. Some samurai also began to take on European-inspired designs by the end of the 16th century.
In all periods, when not in armour, the dress of the samurai didn't vary greatly from the traditional kimono-styled dress - this would be along the lines of that "wandering ronin" look you see in a lot of the Japanese period dramas, like the Kurosawa movies. Most of these are set in the Edo period (17th-19th centuries), when the armour we are talking about was purely ceremonial.