From what I know on the subject, Kithunter has summed up the situation pretty well. There have been a couple of lawsuits brought against propmakers in recent years that I have some knowledge of, both of them by lucasfilm, both of them involving Stormtrooper armour.
The first case was probably about 5 years ago, a guy making trooper suits from his garage and selling them online. A C&D was sent out, he ignored it, and a $1m lawsuit was brought against him. Turned out that the lawyers had gotten a little too eager in their jobs, and with the intervention of a lawyer who was a member of the RPF at the time, the lawsuit was dropped, as long as the original C&D was obeyed. Something like that anyway.
Second case you may well have heard of, Andrew Ainsworth in the UK had the original molds to the stormtrooper helmets and armour, and trading as Shepperton Design Studios (SDS) sold them in large numbers. I believe the number bandied around was he made something like $50k a year from them. Lucasfilm understandably got a little pissy about this, especially given that there was a licensed producer of helmets (MR) at the time, and those kinds of numbers demonstrably affect sales of the licensed product. Lawsuit brought, end result was that he was only allowed to sell the helmets and suits in the UK, where the judge ruled that Lucasfilms copyright on the design had expired.
Bottom line is, stick to low numbers, don't try and pass yourself off as a business churning these out on a production line and don't ask for stupid money, and you're likely to be ok. Places like this, where people obsess over details, make their own stuff and occasionally sell a few copies to help pay for the cost of production, show the studios that the fanbase is alive and well, and they can release official stuff which these same people will buy. I know I still want the licensed stuff!
There are exceptions of course...Anything Trekkie is likely to be smacked down fast by paramount, and they have incurred a fair amount of fan ill will through it. I don't believe sales of the MR Trek stuff was especially great, although linking the two things is of course pure conjecture...
I don't know if I'd bother emailing them, because they're not actually going to put down in writing anything but "Any unlicensed products are in violation of copyright". You'd be dreaming to hope to get an answer like "Don't do too many and we'll overlook it".
I think the agreement is we don't push them, and they won't push back.