No, it doesn't make the remaining shares any more valuable.
Right now the market cap is ~$500 billion, and the liquid assets are known to be about $100B, so the non-liquid asset part of the company is ~$400 billion. When apple buys back the shares, the number of shares in circulation goes down, but so does the market cap, since now it's ~400 billion + ~90 billion assets. These should exactly match. You can imagine this as the board separating out the bits of the company that are apple's ip, employee capital, buildings etc, and the bits of the company that are just the ownership of a huge wadge of cash. They're getting rid of the latter without touching the former.
You would expect this to not impact the share price in itself.