Is it precious to imitate Tang Bohu's calligraphy?

No, it's not precious, but it has market value, because it's hard to tell true from false. There are still people who collect them now, because his original paintings and calligraphy are either in museums or auctioned, and many of them are abroad. What you can collect now is actually hard to distinguish between true and false, and some people are willing to pay a big price for it, so the market value is there.