Theoretically the value of all that cash should be baked into the share price. If shareholders think they can better invest the money, they can sell their shares take their money elsewhere, and only have to pay capital gains tax.
If the companies repatriate the cash, they have to pay tax right now which eats up a substantial percentage. Then they still have to find something to do with the cash. If they pay it out to shareholders there will be an additional dividend tax at the individual level so most shareholders would receive like 50 cents on the dollar for the dollars abroad.
By this logic, every dollar abroad should be worth only 50 cent in the price of a share - after all, that's the real value of that cash after all taxes (contrasted to the accounting value of the dollars on the companies' annual report).
You're right that it's probably discounted somehow by some investors, but it's also worth it's full value if they choose to spend it abroad, so it's not necessarily worth exactly what it would be worth if they repatriated it and paid it out as dividends. The discount depends on what the shareholders think will happen to the money, and I don't think anyone is predicting repatriation any time soon.
Shareholders have to sell the business AND the cash together. That's the concern. If you want to invest in the say 10% ROI business, you have to also invest in the 0% ROI cash hoard at the same time, at a fixed proportion.
If the companies repatriate the cash, they have to pay tax right now which eats up a substantial percentage. Then they still have to find something to do with the cash. If they pay it out to shareholders there will be an additional dividend tax at the individual level so most shareholders would receive like 50 cents on the dollar for the dollars abroad.