Well yeah a lot of it obviously is the same for each quote. There's a lot involved with installing a boiler, we forget that. Tell them about it, why not? I include a works schedule, information about British Standards that will be adhered to, warranty information, cost breakdowns etc etc. They're paying a lot of money, let them know the why it's so much.
I also include printouts about the controls , Magnaclean, powerflushing etc. I include a Vaillant/Worcester brochure with the page marked which has the information about 'their' boiler.
Presentation is everything in every regard. I very often find that a lot of installers forget about actual presentation of the installation itself and how much the customer doesn't even know it's an issue. That's why I take photos of notable installations I do and show them to the customer as an example of my work. This is one that a lot of people seem to like; note the chaos in the first picture. This on purpose to make the final picture seem even 'cleaner'.
http://i.*********/dQa8bqv.jpg
Ones like this are good because you can highlight things like painting the wall first (which I always do) and straight pipes. People love dem straight pipes. It's like hoovering, don't underestimate how much the customer can only quantify what they know (straight pipes, hoovering) as opposed to things they know nothing about (gas, boilers).