Reactivating or scrapping old OSVs

After a long layup, does it pay off to reactivate older OSVs, or is it cheaper and better to scrap and build new, or buy second hand?:

That is a question many owners/operators are facing today, with the market improving worldwide.
If the vessel is 15 years or older it is also a question if charterers are willing to offer any long term charter, even at lower than market rate.

What is your opinion, seen from a US and/or international perspective?