I don't disagree with you about keeper rules distorting value a bit, but that is part of the overall strategy of the league. If people want to gear their drafts towards the future, that is helpful to people trying to win in the current year - that is more and more true the fewer keepers we allow.
I think the best argument for limiting keepers in the first two rounds is that it keeps the draft pool adequate so every has access to at least some good players every year. If you get a top pick but the best 25 players have been kept and you don't have great keepers, that you have the pick is meaningless and the year is basically shot for you.
But if you are going to be truly out of it why wouldn't you trade one of your assets to a contending team for a pick in the draft? Or trade a useful piece for a better keeper option? And even if the best 24 players are kept, then you still have the first option at the best guy available. No one should be objectively rewarded for coming in last. If you are going to struggle that year and the first few weeks prove it, pick up a bunch of young players and hope they return you better value.
But to me by saying you can't keep players in 1st or 2nd to help last place teams, that's just silly. They are still getting the first option out of who is available, and most people will chose not to keep a player in the first over options that provide better ROI. But I still firmly believe everyone should have that option.
Hell, a last place team may have a great keeper option in the 2nd round, which would provide huge value to them as the last pick in the 2nd. If we don't allow first or seconds, then that hurts the worst teams.
(And I don't think you can allow second round keepers and not firsts because of the snake format. You'd have to either allow both - my vote - or neither).