Bit slow on this one, but here goes.
Blackwell Convergence success partially resides on the quality of the previous 2 games. You'll probably find a large stock of sales came from people who invested their time and entertainment in the previous games. I don't know about anyone else, but for me Blackwell 4 is already sold.
In terms of production values and your bottom line, it's not something I can comment on as I don't know the ins and out of your sales figures. Have a look through your previous sales for Blackwell 1 and 2 (I know im being lazy with titles) and match up what information you may have available on buyers to blackwell 3. If most people that bought 1 and 2 first bought 3 next then its clear its the quality of the product itself not the quality of the production.
If I could give you any advice, it would be to maybe put some money into marketing the brand. Send promo copies to games magazines, invest some time and money maybe into popular games websites.
Perhaps a big step in the right direction would be to get your games up on Steam. Also maybe Direct2Drive, Impulse, GOG and a few others that people use.
I think the way forward for your games (and I suppose ultimately the bank account) is to get the products out to a much wider audience. I found you through AGS and via Bestowers of Eternity and Two of a Kind, as did by the looks of things a lot of other members.
On another note, it may also be worthwhile looking at alternative engines for your games. As much as I am a fan of AGS and the games made by it, there is only so much you can do with an old engine. There is probably a big market for these games on other platforms that you should be able to tap into with ease.
In short look at what other indie developers are doing, and make a judgement on what your next step should be. Telltale feature prominently on Steam, and as a result of their success (which arguably is due to them having funds to buy up a popular title by Lucasarts). Hothead Games got their title on Xbox 360.
Just some stuff to ponder over. If you need to talk more about this stuff give me a shout over pm or something. I'm no expert but I'll do my best.