Hi Alasdair, I know this is thread is getting old, but...
I've used stovetops for a a few years...
There isn't really a way of getting a lasting crema, unless you cheat (see below).
I lived in Italy for 3 years, and bialetti style stovetops are used by just about everybody. The received wisdom is that a smallish (about 3 cup) pot will give best results in terms of taste and it is important that it is seasoned... i.e. the more you use the pot the better your coffee will get. If you have a new one, it is common practice to buy a bag of cheap, preground coffee and run through the process about 10 times, not bothering to drink to coffee.
I've heard it said that stainless steel is better than aluminium... I have just got a 2 cup stainless steel bialetti. Still getting used to it.
The stovetop produces a lot less pressure than a proper espresso machine, and I think this is the reason that you can't get a lasting crema (something like it is the emuslion of the oils under the right pressure and at the right temperature being responsible for the creation of the crema). Any attempts to increase the internal pressure by clogging or using finer filters may end in an explosion of hot metal and coffee... not reccommended.
Bialetti has created a stovetop called the Brikka which they claim produces crema, but I can't say I've ever seen it used. It could be that it uses a valve or system such as you might have found in espresso machines a few years ago for creating a sort of pseudo crema (my gran gaggia came with a rubber disk call the sistema crema perfetta)
The 'cheat' way which I learned in Naples depends on your liking sugar in your mokapot coffee. Put enough sugar for all the coffee, plus half a teaspoon, in a wide glass. Dribble in the first coffee to come out of the pot so that it stains all the sugar (but no more). Whisk quickly with a teaspoon until it is foamy and pale. Add this to your coffee (in the cup) and you will get a smooth crema effect.
I am also looking for a low cost, but quality grinder. If you are going to stick with your stove-top you could probably get something cheaper than you would need for a countertop/bar style espresso machine.
I've been scouring ebay and have even looked at ebay Italy. There are some good prices there... How about a vintage grinder for moka pot style for about 40 pounds including postage? See the thread I highjacked...
http://www.toomuchcoffee.com/index.php? ... c&start=15
German ebay seems to have loads of good priced machines and grinders... I don't understand German at all really so not a good option for me...
If you come up with anything brilliant let us know. I'll do the same.