From what I have seen of the Hain campaign finance issues there is very little wrong with the donations apart from the lack of declaration (for the record he was right to quit, he isn't fit to run a department if he can't run his campaign). The Conway story is worse, but not again I am not sure it is real sleaze, especially given how many members are employing family members and the fact that the piss-poor excuse for a Speaker is blocking release of details about this kind of employment.
Solutions to the Hain (and all the other donations scandals) problem have been mentioned by many. As for Conway et al, there are some very easy solutions, firstly we could nationalise the administrative support for MPs, it has issues, it would mean these particular civil servants having to cross the old divide into the political arena. The benefits are obvious, not just a transparent recruitment process and safeguards that the public purse is getting value for money. It would also provide huge benefits to the people working for MPs. This wouldn't stop an MP employing their spouse, but they would have to prove they could do the job. On the other hand we could just take all the money that supports an individual MP, give it to them and them them sort it out, they could keep more of it themselves, but that would mean not having the support there. This would rely on the electorate maintaining the checks and balances and being willing to vote out someone they thought wasn't giving value for money. What I suspect we will get is a waste of money commission that will try and look after the system, but not have all the powers they need so horribly and publicly fail until they try and get their first conviction.