Vests in Guatemala
I just returned from riding Guatemala on Wed Feb 4. I too saw the vests in Guatemala City. That is the only place they are required. You will have no problems with the police.
Guatemala City is not biker friendly for visitors. The city is set up in zones and it is difficult to find your way around. I spent 3 days in Zone 4 (down town) getting the BMW serviced in Dec 2008. It is a good dealership. But getting in and out was spooky. The people are great and they will give directions.
Check out my blog Sampson South Bound
for more details.
I bought insurance in the USA. But no one ever asked for it. It is cheap if you want it. As far as I know it is not required. If you need real information call or contact Dave Drudge or Emma at CATours in Antigua. catours.co.uk
I was up in Quiche and had no security problems. But locals tell me Guatemala City is now dangerous because of gangs. I went to dinner with a local friend in Zone 1, and had no fear.
Hope you have a good trip.