Aldi will open its first city centre store in Manchester next month targeting affluent consumers. It will focus on its premium range, Specially Selected, and its healthy offer, Be Light.
Meanwhile, Lidl and Netto have introduced organic ranges and are also sending out messages that emphasise good value rather than just low price.
The question is: how far can they take it? And will these flirtations with better quality foods help stimulate real growth?
IGD estimates the UK hard discount sector will grow 10% a year until 2010 to take 7.5% market share with sales of £6.2bn. Against a forecast of 2.8% annual growth for the grocery retail industry, that's serious success.
Aldi heads the pack with sales growth of 31% from 2002 to the end of 2006, according to IGD, compared with 27% and 22% for Netto and Lidl respectively. In terms of store numbers, Aldi's will have shot up from 320 to 520 by 2010 compared with Lidl's growth from 430 to 530 and Netto's from 165 to 265.
The inclusion of more upmarket offers but at prices up to 30% cheaper than the big four could mark a step change in growth for the discounters, believes Gavin Rothwell, senior business analyst at IGD.
"The discounters came into the UK having seen opportunities very much at the bottom end of the market.
"They soon found this low price strategy was easily countered by Asda and Tesco with their value ranges. So it's likely they didn't enjoy as much success in the early stages as they had anticipated."
Aldi admitted as much last year, when MD of buying Tony Baines outlined a plan to double its market share to 4.6% by 2010.
The key was to change its image to appeal to middle Britain. At the time he said: "For the past 10 years we haven't got things right. This is the start of a campaign to improve our brand reputation and attract a different type of customer."
That strategy now means quality is more in line with that available at the major supermarkets - but the price differential remains. "The more affluent customer looking for specific quality pays up to 30% less and a customer seeking a bargain pays the price they were looking for but gets better quality," says an Aldi spokeswoman.
Aldi has expanded premium food ranges, experimented with organics and Fairtrade and now offers high ticket non food items such as big-screen LCD TV sets. An ad campaign launched last year, Aldi's first for eight years, highlighted products untypical to discounters such as smoked salmon and Pinot Grigio wine. The company is also upgrading its stores from the grey warehouse look of the Continental discounters and placing them in more affluent areas.
"Aldi has become much more focused on consumer trends. It is becoming much more of a soft discounter as it seeks to appeal to a more affluent consumer," says Steve Gotham, project director at market researcher Allegra Strategies.
And it's working, according to Aldi. "We started a 10-year repositioning programme in 2001 and can certainly see a shift in perception of our brand and products," says the spokeswoman. "We are continuing to expand our ranges and will shortly be launching a new fresh tapas range.
"What we don't offer are 50 different types of ketchup when a customer is looking to buy only one."
Lidl is not far behind. Although it is not pushing as hard as Aldi, it has ramped up its promotional activity, using bogofs and three-for-twos, and has begun testing ethical products, starting with organic eggs.
Gotham says: "Lidl is doing things that would surprise people. One example is its recent test of airline ticket sales through its stores."
Things have not been quite as easy for Netto. Although it is also trying new ranges, such as organic veg, bananas, milk and yoghurt, and is promoting its non food, Netto International MD Claus Juel-Jensen says questions remain about consumer perceptions. "We have always had a value strategy in all the countries in which we operate. But are we communicating this in the UK as well as we can? We have plans to communicate better about our image, but a part of the concept is also to watch costs very closely, so we have to be more basic inside the store than supermarkets."
And that is the discounters' dilemma: how to profess a mainstream offer without raising prices.
The mainstream players will, of course, always put up a fight in a UK grocery market already over its capacity.
Already Asda has opened two Asda Essentials stores, outlets with almost exclusively own brand merchandise, and will announce early next year if it is to open more. Tesco is taking on the discounters in Eastern Europe with its own full-range discounter model, perhaps as a trial of how it may operate a hard discount format here in the UK.
The discounters' upmarket move, meanwhile, is still in its formative stage. "Yes they're introducing premium ranges, Fairtrade and so on," says Rothwell, "but it's still a small proportion of the SKU count in stores. It's not as if the whole offer has switched."
There's more to come, though. Aldi's store at the Arndale Centre in Manchester, which will include lunchtime grab and go ranges as well as premium and healthy offers, signals the chain's intentions. Lidl sold all its fruit and veg at half price last month and is highlighting lines such as crayfish tails and white Bordeaux wine on its website.
And Netto will be working on its communication. "It doesn't help that we can't buy the number of stores we want," says Juel-Jensen, "but we need to get the message to the customer first."
This won't be a worry only for the supermarkets. Kwik Save, which follows a soft discount strategy, will be concerned that while it struggles with availability issues its closest competitors may extend their lead. Although it recently bought back 42 stores from Somerfield, many store managers are concerned it should be getting its house in order first.
Jack Sinclair, a former Safeway director and now development director at SB Capital Europe, wrote in The Grocer earlier this year that "the German discounters are finally breaking through the barrier from budget shoppers to mainstream shoppers.
"Always better on price and often on quality, Aldi and Lidl will start to steal business from the mainstream supermarkets".
Whether or not this happens to the extent it has in Germany, where the discount chains hold 40% market share, its UK share is on the up. Like the stores themselves, in fact.