Well, I feel a little odd posting here, since I'm new to the forums and don't have any practical experience in the industry to pull on other than having talked with a number of mini-sculptors over the years. I'm not going to let my complete and utter ignorance stop me, however, but feel free to disregard it all.
Any problems you are having are clearly not related to your skill or talent; you are a tremendous sculptor. When I first saw your Shae figure in a tutorial on mini sculpting a few years back, my response to the picture was just a simple "wow" before my jaw dropped.
So, your problems are on the business and/or marketing side, and I see a few things, most of which have been at least touched on by other people. Basically, you're dealing with a small niche market, so you have to approach it strategically. This happens to be a niche that is comprised primarily of the following subgroups (insofar as selling minis is concerned):
1. Serious "Display" Painters
2. Gamers who paint
Obviously this is ridiculously oversimplified, and these are not exclusive categories - there are many gamers who are awesome painters, and many "Serious" painters who also game, but in terms of the motivation behind buying a figure, I think these are the two big factors that drive people to buy a particular figure. Although the #1 groups are important to a miniature company because they will sing your praises, give you exposure on sites like Frothers and CMON, and they are consistent buyers. But, when you look at the volume of sales between the two groups, I would bet that #1 is fairly small fraction of total sales. Someone who spends countless hours painting a single figure to perfection only needs to buy a few figures a month to keep busy. A gamer who wants to field a new army needs many more - at least a certain amount to start playing that particular game/faction and even more as they get a feel for tactics and strategy of that game/faction and just generally start to identify themselves with it.
No matter how cool a mini is, a lot of your potential market needs a reason to buy a given figure. Your zO line, for example, was cool as hell, but there was no hook for the #2 people. Now, if you could have made it a zO Bloodbowl team, or started a zO-themed No Quarter army, or something along those lines, then I think your sales would have been higher because you combined the "cool" factor with a practical hook. Even if the customer never actually fields the team or army, once they have an investment in it, they will continue to feed that investment for a while. Because they've invested both time and money into it, that gives them an attachment to the line and an excuse in their own mind for buying them. Remember, this is a hobby, and most people have very finite resources to spend on hobbies, so anything you can do to help them justify the purchase to themselves will help you.
How many times have you heard somebody talk themselves out of a non-essential purchase by saying, "that's cool, but..."?
Don't let them get to the "but" - hit them with both a practical rationale and a coolness factor at the same time, like a one-two combo punch to the brain. "Here's something that's fun to paint, and you can use it to do X". Don't make them think of a practical reason, give them a ready-made one.
Then, once you have a line established, people will look for new releases in that line. They'll justify new purchases because it's part of an army or team, even though their real reason for buying is because you've come up with some new cool take on the concept (Oh, look! Flying Monkey Infantry armed with water buckets FTW!).
You're probably tired of advice, especially from people who have less knowledge of the market than you, so I'll shut up now, but before I do, I want to wish you great luck with whatever you decide to do. I've spent enough time trying to sculpt minis to know just how hard it is. You are a great sculptor and I hope you find the right path for you.