Whats involved with your offline mailout?

I seem to be spending a ridiculous amount of time putting together a letter in the mail to offline clients. I am probably over doing it by analysing their entire site if they have one (assessing design, code quality, meta tags for SEO etc.) or otherwise digging up whatever I can about their business, then formulating the letter based on the results I found.

Is this pretty much what everyone else is doing for their letters? Or is it basically doing a search in Google and generalising until you get an appointment with them?

It sounds like your going over the head of these business owners. They don't care about all that. Focus on results instead.

Sometimes we forget that our jobs have their own "language" and we assume people on the outside of it understands what we are saying.

I'd actually say it's good to customize. I hate getting generic letters; having something written directly, based on what a person sees of my online presence, makes me appreciate the time they spent doing it. It will also generally produce a positive perception and I would be more likely to listen to your suggestions. If someone sends a very brief, or generic message - I put it straight in to spam..