When I insured my home, I specifically requested coverage for my personal belongings in the garage. All they wanted to know was a dollar amount and they added it to the premium - it wasn't too bad. I think it is more the value of the property that they are concerned with more than it's utility. But, when you file a claim, they will want evidence that it was in your possesion - so take pics and document it's value. I only paid a total of about $2400 for my BP but with my time, it would likely cost about $6K to replace with an equivalent machine so that's the value that is on my list - not the purchase price. They depreciate things if/when they pay a claim.....I disagree with this as my BP is almost 50 years old so in their books it is probably worthless.
I would reccomend that you review the contents of your garage and make a list (and photograph) all of your belongings, then come up with replacement costs and compare this to your policy and talk to your agent about your concerns. They might even offer to come out and take a look with you. If your policy only covers $50K in personal property and you have $120K in your garage, ask for an addition to your policy - they will be more than happy to add it for you.
Adding an alarm system to your garage/shop and house will lower your premium, so make sure to ask about that. You can get a really simple-to-install, wireless alarm system from http://www.x10.com/security/wireless_systems.html - this is what I bought for my shop last month - it's an awesome little system and you get a lot of stuff for $150.00.
Also - I have not only been burgalarized, but just this year I had lightning strike my storage shed (not the garage, thank god), catching it on fire and destroying nearly everything in it (Engines, motocross tires, car parts, yard equipment, X-mas stuff). Review your policy and ask questions now, before the fact, so you know what's what.
Sorry for the rant.