This has been debated at great length on other threads. Almost everyone agrees that Liriano is an extremely risky bet. His upside is very high, but the more likely outcome is that he repeats his history and has long periods of terrible pitching.
I think that there are strong arguments to sign him now, and strong arguments to trade him now. With 25 strikeouts in 2 games, his stock is soaring, so both his trade value and the amount that he might accept for a multi-year contract are also soaring.
This is a tough call, but I agree with you that some offer should be made now, before the price goes up even more. My sense is that Liriano may be getting more mature as he grows older, and he may finally be getting his act together. On the other hand, based on Liriano's track record, I am probably wrong.