I see the personal donations as freeing up money for other things. Suppose I have a dress factory and it costs me £10 to make a dress that retails at £500. I donate that dress to Mrs Doodle, leader of the Dog Party.
Mrs Doodle would have to shop for campaign clothes to wear on the telly anyway, so my donation saves them the £500 it could cost to buy the dress in a shop.
This frees up £500 for the Dog Party to spend on posters and clipboards at a cost to me of a tenner, which I can presumably set against tax, and I get publicity for my range of dresses.
So yes, my donation is to Mrs Doodle, but indirectly it funds the Dogs. That's how it works in a number of situations. Charity auctions, raffle prizes, goody bags at PR events, clothes to wear on the red carpet at awards ceremonies - it's not confined to politics.
So long as my dress factory isn't awarded the contract to supply uniforms to the armed forces and the police, and so long as I am not awarded a peerage as a result of my donation, there is no corruption and no case to answer. If I were to become a Baroness, however, or if that huge contract landed in my lap, it would be a very different matter.
If Mrs Doodle's opponents, the Cat party, criticised my (and her) behaviour and complained that it was cash for favours, they would be justified in doing so, if they were free of corruption themselves.
If the dress was worn on the campaign and that was the end of the matter (ie no contract, and no peerage) there is no problem, and it would be perfectly ok for the Dog party to ask questions about the Cats' acceptance of money in return for favours.
If the Cats had accepted donations in return for favours such as huge contracts and peerages and then complained about Mrs Doodle's dress they would be being dishonest and thus setting themselves up for derision when they are exposed.