It puts it on a level with other high-achievers careers - lawyers, consultants, well paid dentists, a whole host of middle-managers. The expenses (yes, including a second housing allowance) are there to make up for the fact that being an MP is a hugely inconvenient job, involving a lot of travel etc. Expenses being abused is another matter entirely, much like defrauding any employer.
In my opinion it's roughly the right salary. I don't see the argument "It's more than the average salary" as being particularly valid, as these are well-educated, intelligent, hard-working people - above average employees and should be paid as such. It makes a lot more sense to compare their salary to the average salaries of those in careers requiring similar levels of success. I can see an argument for it being more, as it is underpaid in the long-term when compared to the progression possible in other, more mercenary careers; however it would be political suicide to bring it before parliament and is therefore unlikely to happen and therefore something I can't be bothered to form a strong opinion about.