The new consoles WILL NOT be £500, the previous ones launched both in a better financial climate and with significantly more expensive hardware. THe 360 wasn't close to £500 to start with, the PS3 was, with a £300+ bluray player on board, the same drives that now cost £30.
R&D for the PS3 chip, and the AMD gpu's in both consoles and to a degree the power PC chip in the 360 would all be significantly more work and more expensive than the current gen. Taking chips that aren't made to work with each other, changing the architecture putting new busses on, modifying for unified mem(in the 360's case) is WAY more expensive than Jaguar/APU and changing them to a far far smaller degree using pieces that have effectively been used before with the main R&D cost for those being paid by AMD for a chip they had already designed.
Either way, currently 360/ps3 sales are individually 3-5 times higher than Wii U sales, a "dead" platform almost is massively outselling a brand new one.
People bought Wii's because they were cheap and everyone had the idea of Star wars and fake lightsabre's and how awesome it would be to play with interactive style controls, they there was Harry Potter, the fad of hoping for realistic Star Wars fighting was long gone. When people HAD a Wii, they bought the few key titles that came out for it, when people don't have a Wii U, they AREN'T going to buy the console just for a few titles.
Thats the Wii U's problem, people will buy a 360 for Halo 3, or 4, but because they also know there will be a dozens of other titles out every year and at least a few of them will likely appeal to the buyer, if not many, and they know they'll be getting the best version of that game. Very very few people buy a £200-500 console for one game alone, or just 4-5 that will only get new(and rehashed) versions every 2-3 years, while any multiplatform release games that do appear on the Wii U, will be significantly inferior versions.
Wii U is in trouble because Wii promised a lot and delivered very little, the massive majority of people I know who got caught in the hype bought it, had Wii Sports, a couple other games, were completely disappointed, bought the odd thoroughly "Nintendo" type title, a Mario or Zelda game here or there, but won't be caught in the trap of buying a Wii again.
You think EA and a whole host of other developers didn't run a few survey's asking who planned to buy a Wii U and saw an overwhelmingly negative response.
AS for E3 making a difference, it really really won't. The massive queues to see anything PS4 or X1, will see the 5 Nintendo games all but forgotten. For any "brand new" title at E3, they'll look a joke compared to the bits shown of the new consoles new games and as such if you say asked people leaving E3 which games there were looking forward to most for the end of the year, you can be damn sure most won't be talking about ANOTHER Mario Kart with crap graphics.
If Nintendo was showcasing 5-10 big Nintendo titles in a year where the PS4/X1 weren't launching they might get some play, but this year, lol, the worst time to be showing off your big 5 titles for a new console to promote sales, is when everyone is clamouring to find out anything about the brand new, MASSIVELY more powerful consoles showing clips, maybe gameplay, (maybe consoles to try?... too early?) that blow the Wii U away. This E3, more than at any time since the original Wii's launch, will show BY FAR the biggest difference in console power, which is the worst possible thing for a Wii U which is badly struggling for sales already.