A VAT increase will reduce the amount everyone spends whatever their budget. I live in Belgium where VAT is currently 21%, so I come back to the UK to buy clothes, or do it online from UK companies; the same for books and CDs and games etc and especially for ds's footwear!
There is also VAT on food here at 6%, so I shop far more frugally here for food than I ever do in the UK. Your money goes twice as far in UK as it does here.
VAT is avoidable to a certain extent depending on what one buys.
You could argue from the other perspective that those who pay tax at 40%, and that is a great deal more than did when Labour came in in 97, due to GB not raising thresholds and allowances, are already contributing a lot proportionally. There comes a point as many on here have pointed out in the past, that it is not sustainable to keep hammering the same people each time for money because they will leave, or retire early, as it won't be worth working and then the burden will fall on those who can afford it least.
You also say it is unfair to take away from those on benefits - I find it astounding that it is possible to have a joint income of up to £66,000 and get tax credits! When ds was a baby, we were earning less than that, paying a mortgage, and shelling out for f/t nursery fees when I went back to work, and tax credits hadn't even been thought of. Interest rates were much higher as well. It is possible to cope without tax credits and I think that Labour should shoulder a lot of the blame for the fact that people can't.