It will certainly attract greedier candidates.
The best argument for a high MP salary is that it makes them harder to bribe - which was indeed a serious problem in UK politics in the C19 and is part of the reason why salaries were introduced in 1911. Unfortunately (or fortunately depending on how you look at it), corruption in the UK is a very different creature now and is largely a function of special interests, lobbying, and party machines. Arguably more damaging in the long term but much harder to uproot. If you let MPs' salaries get too low though then the old problem will resurface...
So there's a balance to be struck between on the one hand encouraging people to go into politics motivated by duty rather than greed (which would suggest keeping them reasonably low) and making them difficult to bribe (which would suggest not keeping it too low...)