The calculus of voter fraud will definitely change. But I don't know. In order for an individual to commit voter fraud, they have to believe that the benefit is worth the risk them as an individual.
And, for the individual, voter fraud would only "work" to the extent that they think everyone else will do it too.
I intuitively feel that voter fraud is a much bigger bogeyman than people make it out to be.
I think the bigger fear is corruption of the election commission; such that they turn a blind eye to or even contribute to voter fraud.
Of course, no system is incorruptible, and the test for acceptance shouldn't be perfection, but improvement over the status quo (this idea of iteration is the cornerstone of our constitution).
That being said, I'm not convinced that the voter fraud risk makes this proposal more corrupt than the system we currently have. Voter fraud is an easier problem to solve than voter suppression, IMO.
Once there is even a suggestion that some state might be increasing its power by encouraging voter fraud, there will be an arms race of other states trying to "counteract" this by encouraging their own voter fraud.
So, if 80% of you 100-seat state votes, 80% voted X and 20% voted Y, you'd get 64 X's and 16 Y's.
This way, both parties are incentivized to vote. Instead of today.
In my opinion, it's harmful to our democracy that members of the "losing party" feel zero incentive to turn out on election day. It encourages disengagement and disillusionment, not to mention the polarization of the electorate.
In Germany, the "crazy parties" get some seats, so their voices are heard. It has a pacification affect on the mainstream parties.
I really like the idea, but I'll volunteer to offer the criticism you'll probably hear.
If a state can give itself more power by counting more votes, then state governments which are confident that their dominant party will win will have a lot of incentive to allow fraudulent votes, and potentially a lot to gain.
For example, if the state government knows that 70% of voters will vote for the Yellow Party, then they can risk encouraging 10% of the population to cast, say, 4 extra votes (for their deceased grandparents), without worrying that the dreaded Purple Party might exploit this laxness and give Purple the win.
Combine that with some selective enforcement (so Purple voters know that, in practice, only they are at risk of prosecution for voter fraud) and the state will be able to magnify its relative strength compared to states that are more scrupulous.