Getting VDB's at all has been very difficults the last few years, but it seems flight loads are picking up this year. SK's IC flights seem to be running at more or less full capacity during the summer months now, i think the cabin factor is over 85% according to the latest company reports.

If was different back in the 90's when i was flying the now defunct SEA-CPH route regularly. It was more often than not that they wanted VDB candidates at the gate back then. Let me just say i financed a lot of leisure trips that way
But the load forecast systems has propably developed a lot since then, so i think the chances are more slim nowadays. During the last 4-5 years of (sporadic) flying, i have never even heard a call for VDBs.

At that time, the standard offer was $600 in flight cupons (redeemable for 1/2 value in cash). I believe it has increased now to 600-800e. They prefer you to be put on another SK flight, for cost reasons i presume.
And i never got anything else than the same service class, so don't hope for upgrades.
And if you have checked luggage, ask already at the check-in if there might be an overbooking situation and if so, let them know you are a VDB candidate so they can load your luggage last. This way, you will be on top of the gate agents list if they know they don't have to dig though the entire cargo hold to unload your bags. This used to be my routine and it worked well.